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Thread: group_by_prio vs multibus - multipath recomend configuration

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  1. group_by_prio vs multibus - multipath recomend configuration

    OS: SLES 11 SP 3

    /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:
    Code:
    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:
    Code:
    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:

    Code:
    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
    }
    Last edited by sharfuddin; 10-Feb-2015 at 12:40.

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