drbdsetup-9.0: Configure the drbd kernel module.

COMMANDS

drbdsetup attach minor lower_dev meta_data_dev meta_data_index,

drbdsetup disk-options minor

The attach command attaches a lower-level device to an existing replicated device. The disk-options command changes the disk options of an attached lower-level device. In either case, the replicated device must have been created with drbdsetup new-minor.

Both commands refer to the replicated device by its minor number. lower_dev is the name of the lower-level device. meta_data_dev is the name of the device containing the metadata, and may be the same as lower_dev. meta_data_index is either a numeric metadata index, or the keyword internal for internal metadata, or the keyword flexible for variable-size external metadata. Available options:

--al-extents extents

DRBD automatically maintains a "hot" or "active" disk area likely to be written to again soon based on the recent write activity. The "active" disk area can be written to immediately, while "inactive" disk areas must be "activated" first, which requires a meta-data write. We also refer to this active disk area as the "activity log".

The activity log saves meta-data writes, but the whole log must be resynced upon recovery of a failed node. The size of the activity log is a major factor of how long a resync will take and how fast a replicated disk will become consistent after a crash.

The activity log consists of a number of 4-Megabyte segments; the al-extents parameter determines how many of those segments can be active at the same time. The default value for al-extents is 1237, with a minimum of 7 and a maximum of 65536.

Note that the effective maximum may be smaller, depending on how you created the device meta data, see also drbdmeta(8) The effective maximum is 919 * (available on-disk activity-log ring-buffer area/4kB -1), the default 32kB ring-buffer effects a maximum of 6433 (covers more than 25 GiB of data) We recommend to keep this well within the amount your backend storage and replication link are able to resync inside of about 5 minutes.

--al-updates {yes | no}

With this parameter, the activity log can be turned off entirely (see the al-extents parameter). This will speed up writes because fewer meta-data writes will be necessary, but the entire device needs to be resynchronized opon recovery of a failed primary node. The default value for al-updates is yes.

--c-delay-target delay_target,

--c-fill-target fill_target,

--c-max-rate max_rate,

--c-plan-ahead plan_time

Dynamically control the resync speed. This mechanism is enabled by setting the c-plan-ahead parameter to a positive value. The goal is to either fill the buffers along the data path with a defined amount of data if c-fill-target is defined, or to have a defined delay along the path if c-delay-target is defined. The maximum bandwidth is limited by the c-max-rate parameter.

The c-plan-ahead parameter defines how fast drbd adapts to changes in the resync speed. It should be set to five times the network round-trip time or more. Common values for c-fill-target for "normal" data paths range from 4K to 100K. If drbd-proxy is used, it is advised to use c-delay-target instead of c-fill-target. The c-delay-target parameter is used if the c-fill-target parameter is undefined or set to 0. The c-delay-target parameter should be set to five times the network round-trip time or more. The c-max-rate option should be set to either the bandwidth available between the DRBD-hosts and the machines hosting DRBD-proxy, or to the available disk bandwidth.

The default values of these parameters are: c-plan-ahead = 20 (in units of 0.1 seconds), c-fill-target = 0 (in units of sectors), c-delay-target = 1 (in units of 0.1 seconds), and c-max-rate = 102400 (in units of KiB/s).

Dynamic resync speed control is available since DRBD 8.3.9.

--c-min-rate min_rate

A node which is primary and sync-source has to schedule application I/O requests and resync I/O requests. The c-min-rate parameter limits how much bandwidth is available for resync I/O; the remaining bandwidth is used for application I/O.

A c-min-rate value of 0 means that there is no limit on the resync I/O bandwidth. This can slow down application I/O significantly. Use a value of 1 (1 KiB/s) for the lowest possible resync rate.

The default value of c-min-rate is 4096, in units of KiB/s.

--disk-barrier,

--disk-flushes,

--disk-drain

DRBD has three methods of handling the ordering of dependent write requests:

disk-barrier

Use disk barriers to make sure that requests are written to disk in the right order. Barriers ensure that all requests submitted before a barrier make it to the disk before any requests submitted after the barrier. This is implemented using 'tagged command queuing' on SCSI devices and 'native command queuing' on SATA devices. Only some devices and device stacks support this method. The device mapper (LVM) only supports barriers in some configurations.

Note that on systems which do not support disk barriers, enabling this option can lead to data loss or corruption. Until DRBD 8.4.1, disk-barrier was turned on if the I/O stack below DRBD did support barriers. Kernels since linux-2.6.36 (or 2.6.32 RHEL6) no longer allow to detect if barriers are supported. Since drbd-8.4.2, this option is off by default and needs to be enabled explicitly.

disk-flushes

Use disk flushes between dependent write requests, also referred to as 'force unit access' by drive vendors. This forces all data to disk. This option is enabled by default.

disk-drain

Wait for the request queue to "drain" (that is, wait for the requests to finish) before submitting a dependent write request. This method requires that requests are stable on disk when they finish. Before DRBD 8.0.9, this was the only method implemented. This option is enabled by default. Do not disable in production environments.

From these three methods, drbd will use the first that is enabled and supported by the backing storage device. If all three of these options are turned off, DRBD will submit write requests without bothering about dependencies. Depending on the I/O stack, write requests can be reordered, and they can be submitted in a different order on different cluster nodes. This can result in data loss or corruption. Therefore, turning off all three methods of controlling write ordering is strongly discouraged.

A general guideline for configuring write ordering is to use disk barriers or disk flushes when using ordinary disks (or an ordinary disk array) with a volatile write cache. On storage without cache or with a battery backed write cache, disk draining can be a reasonable choice.

--disk-timeout

If the lower-level device on which a DRBD device stores its data does not finish an I/O request within the defined disk-timeout, DRBD treats this as a failure. The lower-level device is detached, and the device's disk state advances to Diskless. If DRBD is connected to one or more peers, the failed request is passed on to one of them.

This option is dangerous and may lead to kernel panic!

"Aborting" requests, or force-detaching the disk, is intended for completely blocked/hung local backing devices which do no longer complete requests at all, not even do error completions. In this situation, usually a hard-reset and failover is the only way out.

By "aborting", basically faking a local error-completion, we allow for a more graceful swichover by cleanly migrating services. Still the affected node has to be rebooted "soon".

By completing these requests, we allow the upper layers to re-use the associated data pages.

If later the local backing device "recovers", and now DMAs some data from disk into the original request pages, in the best case it will just put random data into unused pages; but typically it will corrupt meanwhile completely unrelated data, causing all sorts of damage.

Which means delayed successful completion, especially for READ requests, is a reason to panic(). We assume that a delayed *error* completion is OK, though we still will complain noisily about it.

The default value of disk-timeout is 0, which stands for an infinite timeout. Timeouts are specified in units of 0.1 seconds. This option is available since DRBD 8.3.12.

--fencing fencing_policy

Fencing is a preventive measure to avoid situations where both nodes are primary and disconnected. This is also known as a split-brain situation. DRBD supports the following fencing policies:

dont-care

No fencing actions are taken. This is the default policy.

resource-only

If a node becomes a disconnected primary, it tries to fence the peer. This is done by calling the fence-peer handler. The handler is supposed to reach the peer over an alternative communication path and call 'drbdadm outdate minor' there.

resource-and-stonith

If a node becomes a disconnected primary, it freezes all its IO operations and calls its fence-peer handler. The fence-peer handler is supposed to reach the peer over an alternative communication path and call 'drbdadm outdate minor' there. In case it cannot do that, it should stonith the peer. IO is resumed as soon as the situation is resolved. In case the fence-peer handler fails, I/O can be resumed manually with 'drbdadm resume-io'.

--md-flushes

Enable disk flushes and disk barriers on the meta-data device. This option is enabled by default. See the disk-flushes parameter.

--on-io-error handler

Configure how DRBD reacts to I/O errors on a lower-level device. The following policies are defined:

pass_on

Change the disk status to Inconsistent, mark the failed block as inconsistent in the bitmap, and retry the I/O operation on a remote cluster node.

call-local-io-error

Call the local-io-error handler (see the handlers section).

detach

Detach the lower-level device and continue in diskless mode.

--read-balancing policy

Distribute read requests among cluster nodes as defined by policy. The supported policies are prefer-local (the default), prefer-remote, round-robin, least-pending, when-congested-remote, 32K-striping, 64K-striping, 128K-striping, 256K-striping, 512K-striping and 1M-striping.

This option is available since DRBD 8.4.1.

resync-after minor

Define that a device should only resynchronize after the specified other device. By default, no order between devices is defined, and all devices will resynchronize in parallel. Depending on the configuration of the lower-level devices, and the available network and disk bandwidth, this can slow down the overall resync process. This option can be used to form a chain or tree of dependencies among devices.

--resync-rate rate

Define how much bandwidth DRBD may use for resynchronizing. DRBD allows "normal" application I/O even during a resync. If the resync takes up too much bandwidth, application I/O can become very slow. This parameter allows to avoid that. Please note this is option only works when the dynamic resync controller is disabled.

--size size

Specify the size of the lower-level device explicitly instead of determining it automatically. The device size must be determined once and is remembered for the lifetime of the device. In order to determine it automatically, all the lower-level devices on all nodes must be attached, and all nodes must be connected. If the size is specified explicitly, this is not necessary. The size value is assumed to be in units of sectors (512 bytes) by default.

drbdsetup check-resize minor

Remember the current size of the lower-level device of the specified replicated device. Used by drbdadm. The size information is stored in file /var/lib/drbd/drbd-minor-minor.lkbd.

drbdsetup connect resource local_addr remote_addr,

drbdsetup net-options local_addr remote_addr

The connect command connects a resource to a peer host. The resource must have been created with drbdsetup new-resource. The net-options command changes the network options of an existing connection. In both commands, local_addr and remote_addr refer to the local and remote protocol, network address, and port in the format [address-family:]address[:port]. The address families ipv4, ipv6, ssocks (Dolphin Interconnect Solutions' "super sockets"), sdp (Infiniband Sockets Direct Protocol), and sci are supported (sci is an alias for ssocks). If no address family is specified, ipv4 is assumed. For all address families except ipv6, the address uses IPv4 address notation (for example, 1.2.3.4). For ipv6, the address is enclosed in brackets and uses IPv6 address notation (for example, [fd01:2345:6789:abcd::1]). The port defaults to 7788. Available options:

--after-sb-0pri policy

Define how to react if a split-brain scenario is detected and none of the two nodes is in primary role. (We detect split-brain scenarios when two nodes connect; split-brain decisions are always between two nodes.) The defined policies are:

disconnect

No automatic resynchronization; simply disconnect.

discard-younger-primary,

discard-older-primary

Resynchronize from the node which became primary first (discard-younger-primary) or last (discard-older-primary). If both nodes became primary independently, the discard-least-changes policy is used.

discard-zero-changes

If only one of the nodes wrote data since the split brain situation was detected, resynchronize from this node to the other. If both nodes wrote data, disconnect.

discard-least-changes

Resynchronize from the node with more modified blocks.

discard-node-nodename

Always resynchronize to the named node.

--after-sb-1pri policy

Define how to react if a split-brain scenario is detected, with one node in primary role and one node in secondary role. (We detect split-brain scenarios when two nodes connect, so split-brain decisions are always among two nodes.) The defined policies are:

disconnect

No automatic resynchronization, simply disconnect.

consensus

Discard the data on the secondary node if the after-sb-0pri algorithm would also discard the data on the secondary node. Otherwise, disconnect.

violently-as0p

Always take the decision of the after-sb-0pri algorithm, even if it causes an erratic change of the primary's view of the data. This is only useful if a single-node file system (i.e., not OCFS2 or GFS) with the allow-two-primaries flag is used. This option can cause the primary node to crash, and should not be used.

discard-secondary

Discard the data on the secondary node.

call-pri-lost-after-sb

Always take the decision of the after-sb-0pri algorithm. If the decision is to discard the data on the primary node, call the pri-lost-after-sb handler on the primary node.

--after-sb-2pri policy

Define how to react if a split-brain scenario is detected and both nodes are in primary role. (We detect split-brain scenarios when two nodes connect, so split-brain decisions are always among two nodes.) The defined policies are:

disconnect

No automatic resynchronization, simply disconnect.

violently-as0p

See the violently-as0p policy for after-sb-1pri.

call-pri-lost-after-sb

Call the pri-lost-after-sb handler on one of the machines. The handler is expected to reboot the machine, which brings the node into secondary role.

--allow-two-primaries

The most common way to configure DRBD devices is to allow only one node to be primary (and thus writable) at a time.

In some scenarios it is preferable to allow two nodes to be primary at once; a mechanism outside of DRBD then must make sure that writes to the shared, replicated device happen in a coordinated way. This can be done with a shared-storage cluster file system like OCFS2 and GFS, or with virtual machine images and a virtual machine manager that can migrate virtual machines between physical machines.

The allow-two-primaries parameter tells DRBD to allow two nodes to be primary at the same time. Never enable this option when using a non-distributed file system; otherwise, data corruption and node crashes will result!

--always-asbp

Normally the automatic after-split-brain policies are only used if current states of the UUIDs do not indicate the presence of a third node.

With this option you request that the automatic after-split-brain policies are used as long as the data sets of the nodes are somehow related. This might cause a full sync, if the UUIDs indicate the presence of a third node. (Or double faults led to strange UUID sets.)

--connect-int time

As soon as a connection between two nodes is configured with drbdsetup connect, DRBD immediately tries to establish the connection. If this fails, DRBD waits for connect-int seconds and then repeats. The default value of connect-int is 10 seconds.

--cram-hmac-alg hash-algorithm

Configure the hash-based message authentication code (HMAC) or secure hash algorithm to use for peer authentication. The kernel supports a number of different algorithms, some of which may be loadable as kernel modules. See the shash algorithms listed in /proc/crypto. By default, cram-hmac-alg is unset. Peer authentication also requires a shared-secret to be configured.

--csums-alg hash-algorithm

Normally, when two nodes resynchronize, the sync target requests a piece of out-of-sync data from the sync source, and the sync source sends the data. With many usage patterns, a significant number of those blocks will actually be identical.

When a csums-alg algorithm is specified, when requesting a piece of out-of-sync data, the sync target also sends along a hash of the data it currently has. The sync source compares this hash with its own version of the data. It sends the sync target the new data if the hashes differ, and tells it that the data are the same otherwise. This reduces the network bandwidth required, at the cost of higher cpu utilization and possibly increased I/O on the sync target.

The csums-alg can be set to one of the secure hash algorithms supported by the kernel; see the shash algorithms listed in /proc/crypto. By default, csums-alg is unset.

--csums-after-crash-only

Enabling this option (and csums-alg, above) makes it possible to use the checksum based resync only for the first resync after primary crash, but not for later "network hickups".

In most cases, block that are marked as need-to-be-resynced are in fact changed, so calculating checksums, and both reading and writing the blocks on the resync target is all effective overhead.

The advantage of checksum based resync is mostly after primary crash recovery, where the recovery marked larger areas (those covered by the activity log) as need-to-be-resynced, just in case. Introduced in 8.4.5.

--data-integrity-alg alg

DRBD normally relies on the data integrity checks built into the TCP/IP protocol, but if a data integrity algorithm is configured, it will additionally use this algorithm to make sure that the data received over the network match what the sender has sent. If a data integrity error is detected, DRBD will close the network connection and reconnect, which will trigger a resync.

The data-integrity-alg can be set to one of the secure hash algorithms supported by the kernel; see the shash algorithms listed in /proc/crypto. By default, this mechanism is turned off.

Because of the CPU overhead involved, we recommend not to use this option in production environments. Also see the notes on data integrity below.

--ko-count number

If a secondary node fails to complete a write request in ko-count times the timeout parameter, it is excluded from the cluster. The primary node then sets the connection to this secondary node to Standalone. The default value of ko-count is 0, which disables this feature.

--max-buffers number

Limits the memory usage per DRBD minor device on the receiving side, or for internal buffers during resync or online-verify. Unit is PAGE_SIZE, which is 4 KiB on most systems. The minimum possible setting is hard coded to 32 (=128 KiB). These buffers are used to hold data blocks while they are written to/read from disk. To avoid possible distributed deadlocks on congestion, this setting is used as a throttle threshold rather than a hard limit. Once more than max-buffers pages are in use, further allocation from this pool is throttled. You want to increase max-buffers if you cannot saturate the IO backend on the receiving side.

--max-epoch-size number

Define the maximum number of write requests DRBD may issue before issuing a write barrier. The default value is 2048, with a minimum of 1 and a maximum of 20000. Setting this parameter to a value below 10 is likely to decrease performance.

--on-congestion policy,

--congestion-fill threshold,

--congestion-extents threshold

By default, DRBD blocks when the TCP send queue is full. This prevents applications from generating further write requests until more buffer space becomes available again.

When DRBD is used together with DRBD-proxy, it can be better to use the pull-aheadon-congestion policy, which can switch DRBD into ahead/behind mode before the send queue is full. DRBD then records the differences between itself and the peer in its bitmap, but it no longer replicates them to the peer. When enough buffer space becomes available again, the node resynchronizes with the peer and switches back to normal replication.

This has the advantage of not blocking application I/O even when the queues fill up, and the disadvantage that peer nodes can fall behind much further. Also, while resynchronizing, peer nodes will become inconsistent.

The available congestion policies are block (the default) and pull-ahead. The congestion-fill parameter defines how much data is allowed to be "in flight" in this connection. The default value is 0, which disables this mechanism of congestion control, with a maximum of 10 GiBytes. The congestion-extents parameter defines how many bitmap extents may be active before switching into ahead/behind mode, with the same default and limits as the al-extents parameter. The congestion-extents parameter is effective only when set to a value smaller than al-extents.

Ahead/behind mode is available since DRBD 8.3.10.

--ping-int interval

When the TCP/IP connection to a peer is idle for more than ping-int seconds, DRBD will send a keep-alive packet to make sure that a failed peer or network connection is detected reasonably soon. The default value is 10 seconds, with a minimum of 1 and a maximum of 120 seconds. The unit is seconds.

--ping-timeout timeout

Define the timeout for replies to keep-alive packets. If the peer does not reply within ping-timeout, DRBD will close and try to reestablish the connection. The default value is 0.5 seconds, with a minimum of 0.1 seconds and a maximum of 3 seconds. The unit is tenths of a second.

--socket-check-timeout timeout

In setups involving a DRBD-proxy and connections that experience a lot of buffer-bloat it might be necessary to set ping-timeout to an unusual high value. By default DRBD uses the same value to wait if a newly established TCP-connection is stable. Since the DRBD-proxy is usually located in the same data center such a long wait time may hinder DRBD's connect process.

In such setups socket-check-timeout should be set to at least to the round trip time between DRBD and DRBD-proxy. I.e. in most cases to 1.

The default unit is tenths of a second, the default value is 0 (which causes DRBD to use the value of ping-timeout instead). Introduced in 8.4.5.

--protocol name

Use the specified protocol on this connection. The supported protocols are:

Writes to the DRBD device complete as soon as they have reached the local disk and the TCP/IP send buffer.

Writes to the DRBD device complete as soon as they have reached the local disk, and all peers have acknowledged the receipt of the write requests.

Writes to the DRBD device complete as soon as they have reached the local and all remote disks.

--rcvbuf-size size

Configure the size of the TCP/IP receive buffer. A value of 0 (the default) causes the buffer size to adjust dynamically. This parameter usually does not need to be set, but it can be set to a value up to 10 MiB. The default unit is bytes.

--rr-conflict policy

This option helps to solve the cases when the outcome of the resync decision is incompatible with the current role assignment in the cluster. The defined policies are:

disconnect

No automatic resynchronization, simply disconnect.

violently

Resync to the primary node is allowed, violating the assumption that data on a block device are stable for one of the nodes. Do not use this option, it is dangerous.

call-pri-lost

Call the pri-lost handler on one of the machines. The handler is expected to reboot the machine, which puts it into secondary role.

--shared-secret secret

Configure the shared secret used for peer authentication. The secret is a string of up to 64 characters. Peer authentication also requires the cram-hmac-alg parameter to be set.

--sndbuf-size size

Configure the size of the TCP/IP send buffer. Since DRBD 8.0.13 / 8.2.7, a value of 0 (the default) causes the buffer size to adjust dynamically. Values below 32 KiB are harmful to the throughput on this connection. Large buffer sizes can be useful especially when protocol A is used over high-latency networks; the maximum value supported is 10 MiB.

--tcp-cork

By default, DRBD uses the TCP_CORK socket option to prevent the kernel from sending partial messages; this results in fewer and bigger packets on the network. Some network stacks can perform worse with this optimization. On these, the tcp-cork parameter can be used to turn this optimization off.

--timeout time

Define the timeout for replies over the network: if a peer node does not send an expected reply within the specified timeout, it is considered dead and the TCP/IP connection is closed. The timeout value must be lower than connect-int and lower than ping-int. The default is 6 seconds; the value is specified in tenths of a second.

--unplug-watermark number

Mainline kernels before version 2.6.39-rc1 use an explicit plug / unplug mechanism to control when a block device starts processing queued requests. On those kernels, the unplug-watermark parameter defines how many requests must be queued until a secondary node starts processing them. Some storage controllers perform best when unplug-watermark is set to the same value as max-buffers; others are more efficient with smaller values. The default value for unplug-watermark is 128, with a minimum of 16 and a maximum of 131072.

More recent kernels handle plugging and unplugging implicitly; on those kernels, this parameter has no effect. Note that some distributions have backported this feature to older kernel versions.

--use-rle

Each replicated device on a cluster node has a separate bitmap for each of its peer devices. The bitmaps are used for tracking the differences between the local and peer device: depending on the cluster state, a disk range can be marked as different from the peer in the device's bitmap, in the peer device's bitmap, or in both bitmaps. When two cluster nodes connect, they exchange each other's bitmaps, and they each compute the union of the local and peer bitmap to determine the overall differences.

Bitmaps of very large devices are also relatively large, but they usually compress very well using run-length encoding. This can save time and bandwidth for the bitmap transfers.

The use-rle parameter determines if run-length encoding should be used. It is on by default since DRBD 8.4.0.

--verify-alg hash-algorithm

Online verification (drbdadm verify) computes and compares checksums of disk blocks (i.e., hash values) in order to detect if they differ. The verify-alg parameter determines which algorithm to use for these checksums. It must be set to one of the secure hash algorithms supported by the kernel before online verify can be used; see the shash algorithms listed in /proc/crypto.

We recommend to schedule online verifications regularly during low-load periods, for example once a month. Also see the notes on data integrity below.

--discard-my-data

Discard the local data and resynchronize with the peer that has the most up-to-data data. Use this option to manually recover from a split-brain situation.

--tentative

Only determine if a connection to the peer can be established and if a resync is necessary (and in which direction) without actually establishing the connection or starting the resync. Check the system log to see what DRBD would do without the --tentative option.

drbdsetup cstate local_addr remote_addr

Show the current state of a connection. The connection is identified by its endpoints; see the drbdsetup connect command.

drbdsetup del-minor minor

Remove a replicated device. No lower-level device may be attached; see drbdsetup detach.

drbdsetup del-resource resource

Remove a resource. All volumes and connections must be removed first (drbdsetup del-minor, drbdsetup disconnect). Alternatively, drbdsetup down can be used to remove a resource together with all its volumes and connections.

drbdsetup detach minor

Detach the lower-level device of a replicated device. Available options:

--force

Force the detach and return immediately. This puts the lower-level device into failed state until all pending I/O has completed, and then detaches the device. Any I/O not yet submitted to the lower-level device (for example, because I/O on the device was suspended) is assumed to have failed.

drbdsetup disconnect local_addr remote_addr

Remove a connection to a peer host. The connection is identified by its endpoints; see the drbdsetup connect command.

drbdsetup down {resource | all}

Take a resource down by removing all volumes, connections, and the resource itself.

drbdsetup dstate minor

Show the current disk state of a lower-level device.

drbdsetup events2 {resource | all}

Show the current state of all configured DRBD objects, followed by all changes to the state.

The output format is meant to be human as well as machine readable. Each line starts with the event number, which is followed by an asterisk if the event continues in the next line. The second word in each line indicates the kind of event: exists for an existing object; create, destroy, and change if an object is created, destroyed, or changed; or call or response if an event handler is called or it returns. The third word indicates the object the event applies to: resource, device, connection, peer-device, helper, or a dash (-) to indicate that the current state has been dumped completely.

The remaining words identify the object and describe the state that he object is in. Available options:

--now

Terminate after reporting the current state. The default is to continuously listen and report state changes.

--statistics

Include statistics in the output.

drbdsetup get-gi volume local_addr remote_addr

Show the data generation identifiers for a device on a particular connection. The device is identified by its volume number. The connection is identified by its endpoints; see the drbdsetup connect command.

The output consists of the current UUID, bitmap UUID, and the first two history UUIDS, folowed by a set of flags. The current UUID and history UUIDs are device specific; the bitmap UUID and flags are peer device specific. This command only shows the first two history UUIDs. Internally, DRBD maintains one history UUID for each possible peer device.

drbdsetup invalidate minor

Replace the local data of a device with that of a peer. All the local data will be marked out-of-sync, and a resync with the specified peer device will be initialted.

drbdsetup invalidate-remote volume local_addr remote_addr

Replace a peer device's data of a resource with the local data. The peer device's data will be marked out-of-sync, and a resync from the local node to the specified peer will be initiated.

drbdsetup new-current-uuid minor

Generate a new current UUID and rotates all other UUID values. This has at least two use cases, namely to skip the initial sync, and to reduce network bandwidth when starting in a single node configuration and then later (re-)integrating a remote site.

Available option:

--clear-bitmap

Clears the sync bitmap in addition to generating a new current UUID.

This can be used to skip the initial sync, if you want to start from scratch. This use-case does only work on "Just Created" meta data. Necessary steps:

On both nodes, initialize meta data and configure the device.

drbdadm create-md --force res

They need to do the initial handshake, so they know their sizes.

drbdadm up res

They are now Connected Secondary/Secondary Inconsistent/Inconsistent. Generate a new current-uuid and clear the dirty bitmap.

drbdadm --clear-bitmap new-current-uuid res

They are now Connected Secondary/Secondary UpToDate/UpToDate. Make one side primary and create a file system.

drbdadm primary res

mkfs -t fs-type $(drbdadm sh-dev res)

One obvious side-effect is that the replica is full of old garbage (unless you made them identical using other means), so any online-verify is expected to find any number of out-of-sync blocks.

You must not use this on pre-existing data! Even though it may appear to work at first glance, once you switch to the other node, your data is toast, as it never got replicated. So do not leave out the mkfs (or equivalent).

This can also be used to shorten the initial resync of a cluster where the second node is added after the first node is gone into production, by means of disk shipping. This use-case works on disconnected devices only, the device may be in primary or secondary role.

The necessary steps on the current active server are:

drbdsetup new-current-uuid --clear-bitmap minor

Take the copy of the current active server. E.g. by pulling a disk out of the RAID1 controller, or by copying with dd. You need to copy the actual data, and the meta data.

drbdsetup new-current-uuid minor

Now add the disk to the new secondary node, and join it to the cluster. You will get a resync of that parts that were changed since the first call to drbdsetup in step 1.

drbdsetup new-minor resource minor volume

Create a new replicated device within a resource. The command creates a block device inode for the replicated device (by default, /dev/drbdminor). The volume number identifies the device within the resource.

drbdsetup new-resource resource node_id,

drbdsetup resource-options resource

The new-resource command creates a new resource. The resource-options command changes the resource options of an existing resource. Available options:

--auto-promote bool-value

A resource must be promoted to primary role before any of its devices can be mounted or opened for writing.

Before DRBD 9, this could only be done explicitly ("drbdadm primary"). Since DRBD 9, the auto-promote parameter allows to automatically promote a resource to primary role when one of its devices is mounted or opened for writing. As soon as all devices are unmounted or closed with no more remaining users, the role of the resource changes back to secondary.

Automatic promotion only succeeds if the cluster state allows it (that is, if an explicit drbdadm primary command would succeed). Otherwise, mounting or opening the device fails as it already did before DRBD 9: the mount(2) system call fails with errno set to EROFS (Read-only file system); the open(2) system call fails with errno set to EMEDIUMTYPE (wrong medium type).

Irrespective of the auto-promote parameter, if a device is promoted explicitly (drbdadm primary), it also needs to be demoted explicitly (drbdadm secondary).

The auto-promote parameter is available since DRBD 9.0.0, and defaults to yes.

--cpu-mask cpu-mask

Set the cpu affinity mask for DRBD kernel threads. The cpu mask is specified as a hexadecimal number. The default value is 0, which lets the scheduler decide which kernel threads run on which CPUs. CPU numbers in cpu-mask which do not exist in the system are ignored.

--on-no-data-accessible policy

Determine how to deal with I/O requests when the requested data is not available locally or remotely (for example, when all disks have failed). The defined policies are:

io-error

System calls fail with errno set to EIO.

suspend-io

The resource suspends I/O. I/O can be resumed by (re)attaching the lower-level device, by connecting to a peer which has access to the data, or by forcing DRBD to resume I/O with drbdadm resume-io res. When no data is available, forcing I/O to resume will result in the same behavior as the io-error policy.

This setting is available since DRBD 8.3.9; the default policy is io-error.

--peer-ack-window value

On each node and for each device, DRBD maintains a bitmap of the differences between the local and remote data for each peer device. For example, in a three-node setup (nodes A, B, C) each with a single device, every node maintains one bitmap for each of its peers.

When nodes receive write requests, they know how to update the bitmaps for the writing node, but not how to update the bitmaps between themselves. In this example, when a write request propagates from node A to B and C, nodes B and C know that they have the same data as node A, but not whether or not they both have the same data.

As a remedy, the writing node occasionally sends peer-ack packets to its peers which tell them which state they are in relative to each other.

The peer-ack-window parameter specifies how much data a primary node may send before sending a peer-ack packet. A low value causes increased network traffic; a high value causes less network traffic but higher memory consumption on secondary nodes and higher resync times between the secondary nodes after primary node failures. (Note: peer-ack packets may be sent due to other reasons as well, e.g. membership changes or expiry of the peer-ack-delay timer.)

The default value for peer-ack-window is 2 MiB, the default unit is sectors. This option is available since 9.0.0.

--peer-ack-delay expiry-time

If after the last finished write request no new write request gets issued for expiry-time, then a peer-ack packet is sent. If a new write request is issued before the timer expires, the timer gets reset to expiry-time. (Note: peer-ack packets may be sent due to other reasons as well, e.g. membership changes or the peer-ack-window option.)

This parameter may influence resync behavior on remote nodes. Peer nodes need to wait until they receive an peer-ack for releasing a lock on an AL-extent. Resync operations between peers may need to wait for for these locks.

The default value for peer-ack-delay is 100 milliseconds, the default unit is milliseconds. This option is available since 9.0.0.

drbdsetup outdate minor

Mark the data on a lower-level device as outdated. This is used for fencing, and prevents the resource the device is part of from becoming primary in the future. See the --fencing disk option.

drbdsetup pause-sync volume local_addr remote_addr

Stop resynchronizing between a local and a peer device by setting the local pause flag. The resync can only resume if the pause flags on both sides of a connection are cleared.

drbdsetup primary resource

Change the role of a node in a resource to primary. This allows the replicated devices in this resource to be mounted or opened for writing. Available options:

--overwrite-data-of-peer

This option is an alias for the --force option.

--force

Force the resource to become primary even if some devices are not guaranteed to have up-to-date data. This option is used to turn one of the nodes in a newly created cluster into the primary node, or when manually recovering from a disaster.

Note that this can lead to split-brain scenarios. Also, when forcefully turning an inconsistent device into an up-to-date device, it is highly recommended to use any integrity checks available (such as a filesystem check) to make sure that the device can at least be used without crashing the system.

Note that DRBD usually only allows one node in a cluster to be in primary role at any time; this allows DRBD to coordinate access to the devices in a resource across nodes. The --allow-two-primaries network option changes this; in that case, a mechanism outside of DRBD needs to coordinate device access.

drbdsetup resize minor

Reexamine the size of the lower-level devices of a replicated device on all nodes. This command is called after the lower-level devices on all nodes have been grown to adjust the size of the replicated device. Available options:

--assume-peer-has-space

Resize the device even if some of the peer devices are not connected at the moment. DRBD will try to resize the peer devices when they next connect. It will refuse to connect to a peer device which is too small.

--assume-clean

Do not resynchronize the added disk space; instead, assume that it is identical on all nodes. This option can be used when the disk space is uninitialized and differences do not matter, or when it is known to be identical on all nodes. See the drbdsetup verify command.

--size val

This option can be used to online shrink the usable size of a drbd device. It's the users responsibility to make sure that a file system on the device is not truncated by that operation.

--al-stripes val --al-stripes val

These options may be used to change the layout of the activity log online. In case of internal meta data this may invovle shrinking the user visible size at the same time (unsing the --size) or increasing the avalable space on the backing devices.

drbdsetup resume-io minor

Resume I/O on a replicated device. See the --fencing disk option.

drbdsetup resume-sync volume local_addr remote_addr

Allow resynchronization to resume by clearing the local sync pause flag.

drbdsetup role resource

Show the current role of a resource.

drbdsetup secondary resource

Change the role of a node in a resource to secondary. This command fails if the replicated device is in use.

drbdsetup show {resource | all}

Show the current configuration of a resource, or of all resources. Available options:

--show-defaults

Show all configuration parameters, even the ones with default values. Normally, parameters with default values are not shown.

drbdsetup show-gi volume local_addr remote_addr

Show the data generation identifiers for a device on a particular connection. In addition, explain the output. The output otherwise is the same as in the drbdsetup get-gi command.

drbdsetup state

This is an alias for drbdsetup role. Deprecated.

drbdsetup status {resource | all}

Show the status of a resource, or of all resources. The output consists of one paragraph for each configured resource. Each paragraph contains one line for each resource, followed by one line for each device, and one line for each connection. The device and connection lines are indented. The connection lines are followed by one line for each peer device; these lines are indented against the connection line.

Long lines are wrapped around at terminal width, and indented to indicate how the lines belongs together. Available options:

--verbose

Include more information in the output even when it is likely redundant or irrelevant.

--statistics

Include data transfer statistics in the output.

--color={always | auto | never}

Colorize the output. With --color=auto, drbdsetup emits color codes only when standard output is connected to a terminal.

For example, the non-verbose output for a resource with only one connection and only one volume could look like this:

drbd0 role:Primary
  disk:UpToDate
  host2.example.com role:Secondary
    disk:UpToDate

With the --verbose option, the same resource could be reported as:

drbd0 node-id:1 role:Primary suspended:no
  volume:0 minor:1 disk:UpToDate blocked:no
  host2.example.com local:ipv4:192.168.123.4:7788
      peer:ipv4:192.168.123.2:7788 node-id:0 connection:WFReportParams
      role:Secondary congested:no
    volume:0 replication:Connected disk:UpToDate resync-suspended:no

drbdsetup suspend-io minor

Suspend I/O on a replicated device. It is not usually necessary to use this command.

drbdsetup verify volume local_addr remote_addr

Start online verification, change which part of the device will be verified, or stop online verification. The command requires the specified peer to be connected.

Online verification compares each disk block on the local and peer node. Blocks which differ between the nodes are marked as out-of-sync, but they are not automatically brought back into sync. To bring them into sync, the resource must be disconnected and reconnected. Progress can be monitored in the output of drbdsetup status --statistics. Available options:

--start position

Define where online verification should start. This parameter is ignored if online verification is already in progress. If the start parameter is not specified, online verification will continue where it was interrupted (if the connection to the peer was lost while verifying), after the previous stop sector (if the previous online verification has finished), or at the beginning of the device (if the end of the device was reached, or online verify has not run before).

The position on disk is specified in disk sectors (512 bytes) by default.

--stop position

Define where online verification should stop. If online verification is already in progress, the stop position of the active online verification process is changed. Use this to stop online verification.

The position on disk is specified in disk sectors (512 bytes) by default.

Also see the notes on data integrity in the drbd.conf(5) manual page.

drbdsetup wait-connect-volume volume local_addr remote_addr,

drbdsetup wait-connect-connection resource local_addr remote_addr,

drbdsetup wait-connect-resource resource,

drbdsetup wait-sync-volume volume local_addr remote_addr,

drbdsetup wait-sync-connection resource local_addr remote_addr,

drbdsetup wait-sync-resource resource

The wait-connect-* commands waits until a device on a peer is visible. The wait-sync-* commands waits until a device on a peer is up to date. Available options for both commands:

--degr-wfc-timeout timeout

Define how long to wait until all peers are connected in case the cluster consisted of a single node only when the system went down. This parameter is usually set to a value smaller than wfc-timeout. The assumption here is that peers which were unreachable before a reboot are less likely to be be reachable after the reboot, so waiting is less likely to help.

The timeout is specified in seconds. The default value is 0, which stands for an infinite timeout. Also see the wfc-timeout parameter.

--outdated-wfc-timeout timeout

Define how long to wait until all peers are connected if all peers were outdated when the system went down. This parameter is usually set to a value smaller than wfc-timeout. The assumption here is that an outdated peer cannot have become primary in the meantime, so we don't need to wait for it as long as for a node which was alive before.

The timeout is specified in seconds. The default value is 0, which stands for an infinite timeout. Also see the wfc-timeout parameter.

--wait-after-sb

This parameter causes DRBD to continue waiting in the init script even when a split-brain situation has been detected, and the nodes therefore refuse to connect to each other.

--wfc-timeout timeout

Define how long the init script waits until all peers are connected. This can be useful in combination with a cluster manager which cannot manage DRBD resources: when the cluster manager starts, the DRBD resources will already be up and running. With a more capable cluster manager such as Pacemaker, it makes more sense to let the cluster manager control DRBD resources. The timeout is specified in seconds. The default value is 0, which stands for an infinite timeout. Also see the degr-wfc-timeout parameter.

drbdsetup forget-peer resource peer_node_id

The forget-peer command removes all traces of a peer node from the meta-data. It frees a bitmap slot in the meta-data and make it avalable for futher bitmap slot allocation in case a so-far never seen node connects.

The connection must be taken down before this command may be used. In case the peer re-connects at a later point a bit-map based resync will be turned into a full-sync.

drbdsetup-9.0 (8)

SYNOPSIS

DESCRIPTION

COMMANDS

EXAMPLES

VERSION

AUTHOR

REPORTING BUGS

COPYRIGHT

RELATED TO drbdsetup-9.0…

NOTES