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How To Configure Fiber Channel Multipath in Linux

Support Team
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Introduction

This article explains the required settings for multipath.conf when utilizing Linux as an initiator for fiber / fibre channel access to a VPSA, to ensure I/O is sent to the correct paths and failovers are handled properly.

Zadara VPSAs have two controllers, an active, and a standby (which can be seen in the "Controllers" section of the GUI).  Each controller has two fiber channel paths to the fiber channel switches - one to each switch in the redundant pair.  This means all initiators to the Zadara VPSA will have 4 paths - 2 to the active controller, and two to the standby controller.

All I/O must be sent only to the active controller, as it is the only controller that can service I/O requests.  Paths to the standby controller should be connected, but in a standby state should a failover occur.

Multipath Configuration

The following configuration should be included in your system's multipath configuration file - generally found at /etc/multipath.conf.

Config

# Use the blacklist section to exclude local disks from being handled
# by multipath-tools.  It is possible to blacklist by vendor/product
# (with regular expressions), devnode (with regular expressions), WWID.
# Below is an example, for more info see "man multipath.conf"

blacklist {
    device {
        vendor "QEMU"
        product "*"
    }
}

# The below section will handle Zadara volumes

devices {

    device {

        vendor "Zadara"
        product "VPSA"
        path_grouping_policy group_by_prio
        path_checker tur
        features "0"
        hardware_handler "1 alua"
        prio alua

        failback immediate
        no_path_retry 10
        rr_min_io 1
    }
}

Sample Output

After applying the above configuration to the multipath.conf file and reloading the multipath service, running the command "multipath -ll" should show output similar to the following:

multipath -ll
2346631646263392d dm-4 Zadara,VPSA
size=4.0T features='0' hwhandler='1 alua' wp=rw
|-+- policy='round-robin 0' prio=50 status=active
| |- 1:0:0:4 sdf 8:80  active ready running
| `- 2:0:0:4 sdp 8:240 active ready running
`-+- policy='round-robin 0' prio=1 status=enabled
  |- 1:0:1:4 sdk 8:160 active ready running
  `- 2:0:1:4 sdu 65:64 active ready running
26164303262306538 dm-2 Zadara,VPSA
size=6.0T features='0' hwhandler='1 alua' wp=rw
|-+- policy='round-robin 0' prio=50 status=active
| |- 1:0:0:2 sdd 8:48  active ready running
| `- 2:0:0:2 sdn 8:208 active ready running
`-+- policy='round-robin 0' prio=1 status=enabled
  |- 1:0:1:2 sdi 8:128 active ready running
  `- 2:0:1:2 sds 65:32 active ready running
26265613032383966 dm-1 Zadara,VPSA
size=6.0T features='0' hwhandler='1 alua' wp=rw
|-+- policy='round-robin 0' prio=50 status=active
| |- 1:0:0:1 sdc 8:32  active ready running
| `- 2:0:0:1 sdm 8:192 active ready running
`-+- policy='round-robin 0' prio=1 status=enabled
  |- 1:0:1:1 sdh 8:112 active ready running
  `- 2:0:1:1 sdr 65:16 active ready running
26630326134393433 dm-3 Zadara,VPSA
size=2.0T features='0' hwhandler='1 alua' wp=rw
|-+- policy='round-robin 0' prio=50 status=active
| |- 1:0:0:3 sde 8:64  active ready running
| `- 2:0:0:3 sdo 8:224 active ready running
`-+- policy='round-robin 0' prio=1 status=enabled
  |- 1:0:1:3 sdj 8:144 active ready running
  `- 2:0:1:3 sdt 65:48 active ready running
23861343738303036 dm-0 Zadara,VPSA
size=20G features='0' hwhandler='1 alua' wp=rw
|-+- policy='round-robin 0' prio=50 status=active
| |- 1:0:0:0 sdb 8:16  active ready running
| `- 2:0:0:0 sdl 8:176 active ready running
`-+- policy='round-robin 0' prio=1 status=enabled
  |- 1:0:1:0 sdg 8:96  active ready running
  `- 2:0:1:0 sdq 65:0  active ready running

Please note that for each mounted multipath volume, there should be two paths that are
"status=active" and two that are "status=enabled".  The "status=active" are the paths to
the active virtual controller, and the "status=enabled" are the paths to the standby.  I/O
will only go to the "active" paths - and should a failover occur, the ALUA mechanism will
handle the switch to the other controller automatically.

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