multipath recommended configuration

[csrsupport]

OS: SLES 11 SP 3 (kernel version: 3.0.x)

/dev/dm-0 comprises of sdg, sdq AND sdb, sdl

If "path_grouping_policy" is set to "group_by_prio" then I observe(via iostat -xk /dev/dm-0) all I/O only on /dev/sdg and /dev/sdq, while sdb and sdl remains 100% idle.
But when "path_grouping_policy" is set to "multibus", then I can see that I/O is properly distributed on all the disks(sdg, sdq .. sdb, sdl).

when "path_grouping_policy" is set to "group_by_prio" then running "multipath -ll" shows:

mpatha (3600c0ff0001e6435600e9b5401000000) dm-0 HP,MSA 2040 SAN
size=2.2T features='1 queue_if_no_path' hwhandler='0' wp=rw
|-+- policy='round-robin 0' prio=50 status=active
| |- 3:0:1:0  sdg 8:96  active ready running
| `- 4:0:1:0  sdq 65:0  active ready running
`-+- policy='round-robin 0' prio=10 status=enabled
  |- 3:0:0:0  sdb 8:16  active ready running
  `- 4:0:0:0  sdl 8:176 active ready running

 when "path_grouping_policy" is set to "multibus" then running "multipath -ll" shows:

mpatha (3600c0ff0001e6435600e9b5401000000) dm-0 HP,MSA 2040 SAN
size=2.2T features='1 queue_if_no_path' hwhandler='0' wp=rw
`-+- policy='round-robin 0' prio=30 status=active
  |- 3:0:0:0  sdb 8:16  active ready running
  |- 3:0:1:0  sdg 8:96  active ready running
  |- 4:0:0:0  sdl 8:176 active ready running
  `- 4:0:1:0  sdq 65:0  active ready running

Please recommend me which one is recommended for best performance(group_by_prio vs multibus). Also /etc/multipath.conf on my system looks like:

defaults {
            polling_interval       10
            path_selector          "round-robin 0"
            path_grouping_policy   group_by_prio
            uid_attribute          "ID_SERIAL"
            prio                   alua   
            path_checker           tur    
            rr_min_io_rq           100
            flush_on_last_del      no
            max_fds                "max"
            rr_weight              uniform   
            failback               immediate
            no_path_retry          18    
            queue_without_daemon   no
            user_friendly_names    yes
            mode                   644
            uid                    0
            gid                    disk
}

Also is there any multipath driver available from HP for MSA 2040 for Linux(RHEL 7 and SLES 11 SP 3) ?

Regards,

[Alzhy]

The MSA array is NOT an Active-Active Array.

So expect not all four sub-paths (sdXX) will be active. The array is active-passive so expect I/O to be on half the active paths only...

Let me know if this clarifies the issue.

[NAP_All41]

I managed to get both sp's active\active..  Just playing around with some perf tests to see if "round-robin" or "queue-lenght 0" works best. 

[root@-xen-01 ~]# multipath -ll
3600c0ff000296ed90974245a01000000 dm-1 HP ,MSA 2040 SAN
size=931G features='0' hwhandler='1 alua' wp=rw
`-+- policy='queue-length 0' prio=1 status=active
|- 1:0:1:1 sdc 8:32 active ready running
|- 1:0:3:1 sde 8:64 active ready running
|- 2:0:1:2 sdg 8:96 active ready running
`- 2:0:3:2 sdi 8:128 active ready running
3600c0ff000299fb77eeb245a01000000 dm-0 HP ,MSA 2040 SAN
size=931G features='0' hwhandler='1 alua' wp=rw
`-+- policy='queue-length 0' prio=1 status=active
|- 1:0:0:1 sdb 8:16 active ready running
|- 1:0:2:1 sdd 8:48 active ready running
|- 2:0:0:2 sdf 8:80 active ready running
`- 2:0:2:2 sdh 8:112 active ready running
[root@xxx-xen-01 ~]#

device {
vendor "HP "
product "MSA 2040 SAN "
hardware_handler "1 alua"
path_selector "queue-length 0"
path_grouping_policy multibus
failback immediate
path_checker hp_sw
rr_weight priorities

__________________________________

round robin alua

[root@xxx-xen-02 sbin]# multipath -ll
3600c0ff000296ed90974245a01000000 dm-0 HP ,MSA 2040 SAN
size=931G features='0' hwhandler='1 alua' wp=rw
`-+- policy='round-robin 0' prio=1 status=active
|- 1:0:0:1 sdg 8:96 active ready running
|- 2:0:0:2 sdf 8:80 active ready running
|- 1:0:1:1 sde 8:64 active ready running
`- 2:0:3:2 sdi 8:128 active ready running
3600c0ff000299fb77eeb245a01000000 dm-1 HP ,MSA 2040 SAN
size=931G features='0' hwhandler='1 alua' wp=rw
`-+- policy='round-robin 0' prio=1 status=active
|- 1:0:2:1 sdd 8:48 active ready running
|- 2:0:1:2 sdb 8:16 active ready running
|- 1:0:3:1 sdc 8:32 active ready running
`- 2:0:2:2 sdh 8:112 active ready running
[root@xxx-xen-02 sbin]#

________________________________

device {
vendor "HP "
product "MSA 2040 SAN "
hardware_handler "1 alua"
path_selector "round-robin 0"
path_grouping_policy multibus
failback immediate
path_checker tur
rr_weight priorities