mrsas4

Usage

Overview

The mrsas driver will detect Broadcom/LSI's 6Gb/s and 12Gb/s PCI Express SAS/SATA/NVMe RAID controllers. A disk (virtual disk/physical disk) attached to the mrsas driver will be visible to the user through camcontrol(8) as /dev/da? device nodes. A simple management interface is also provided per-controller via the /dev/mrsas? device node.

The mrsas name is derived from the phrase "MegaRAID SAS HBA", which is substantially different than the old "MegaRAID" Driver mfi(4) which does not connect targets to the cam(4) layer and thus requires a new driver which attaches targets to the cam(4) layer. Older MegaRAID controllers are supported by mfi(4) and will not work with mrsas, but both the mfi(4) and mrsas drivers can detect and manage the Broadcom/LSI MegaRAID SAS 2208/2308/3008/3108 series of controllers.

The device.hints(5) option is provided to tune the mrsas driver's behavior for LSI MegaRAID SAS 2208/2308/3008/3108 controllers. By default, the mfi(4) driver will detect these controllers. See the PRIORITY section to know more about driver priority for MR-Fusion devices.

mrsas will provide a priority of (-30) (between BUS_PROBE_DEFAULT and BUS_PROBE_LOW_PRIORITY) at probe call for device id's 0x005B, 0x005D, and 0x005F so that mrsas does not take control of these devices without user intervention.

Solid-state drives (SSD) get ATA TRIM support with mrsas if underlying adapter allows it. This may require configuring SSD as Non-RAID drive rather then JBOD virtual mode.

Hardware

The mrsas driver supports the following Broadcom/LSI SATA/SAS RAID controllers:

Configuration

To disable Online Controller Reset(OCR) for a specific mrsas driver instance, set the following tunable value in loader.conf(5):

dev.mrsas.X.disable_ocr=1

where X is the adapter number.

To change the I/O timeout value for a specific mrsas driver instance, set the following tunable value in loader.conf(5):

dev.mrsas.X.mrsas_io_timeout=NNNNNN

where NNNNNN is the timeout value in milli-seconds.

To change the firmware fault check timer value for a specific mrsas driver instance, set the following tunable value in loader.conf(5):

dev.mrsas.X.mrsas_fw_fault_check_delay=NN

where NN is the fault check delay value in seconds.

The current number of active I/O commands is shown in the dev.mrsas.X.fw_outstanding sysctl(8) variable.

Debugging

To enable debugging prints from the mrsas driver, set the hw.mrsas.X.debug_level variable, where X is the adapter number, either in loader.conf(5) or via sysctl(8). The following bits have the described effects:

0x01

Enable informational prints.

0x02

Enable tracing prints.

0x04

Enable prints for driver faults.

0x08

Enable prints for OCR and I/O timeout.

0x10

Enable prints for AEN events.

Priority

The mrsas driver will always set a default (-30) priority in the PCI subsystem for selection of MR-Fusion cards. (It is between BUS_PROBE_DEFAULT and BUS_PROBE_LOW_PRIORITY). MR-Fusion Controllers include all cards with the Device IDs - 0x005B, 0x005D, 0x005F.

The mfi(4) driver will set a priority of either BUS_PROBE_DEFAULT or BUS_PROBE_LOW_PRIORITY (depending on the device.hints setting) in the PCI subsystem for selection of MR-Fusion cards. With the above design in place, the mfi(4) driver will attach to a MR-Fusion card given that it has a higher priority than mrsas.

Using /boot/device.hints (as mentioned below), the user can provide a preference for the mrsas driver to detect a MR-Fusion card instead of the mfi(4) driver.

At boot time, the mfi(4) driver will get priority to detect MR-Fusion controllers by default. Before changing this default driver selection policy, LSI advises users to understand how the driver selection policy works. LSI's policy is to provide priority to the mfi(4) driver to detect MR-Fusion cards, but allow for the ability to choose the mrsas driver to detect MR-Fusion cards.

LSI recommends setting hw.mfi.mrsas_enable="0" for customers who are using the older mfi(4) driver and do not want to switch to mrsas. For those using a MR-Fusion controller for the first time, LSI recommends using the mrsas driver and setting hw.mfi.mrsas_enable="1".

Changing the default behavior is well tested under most conditions, but unexpected behavior may pop up if more complex and unrealistic operations are executed by switching between the mfi(4) and mrsas drivers for MR-Fusion. Switching drivers is designed to happen only one time. Although multiple switching is possible, it is not recommended. The user should decide from boot which driver they want to use for the MR-Fusion card.

The user may see different device names when switching from mfi(4) to mrsas. This behavior works as intended and the user needs to change the fstab(5) entry manually if they are doing any experiments with mfi(4) and mrsas interoperability.

Files

/dev/da?

array/logical disk interface

/dev/mrsas?

management interface

Caveats

The mrsas driver exposes devices as /dev/da?, whereas mfi(4) exposes devices as /dev/mfid?.

mrsas does not support the Linux Emulator Interface, mfiutil(8), or device name aliases for switching drivers without editing fstab(5).