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Re: [dm-devel] General and configuration questions



Allen, Jack [Jack Allen mckesson com] wrote:
>    Hello:
>            I have a system with 2 paths to the SAN which is HITACHI HP. The
>    output of multipath -ll is:
> 
>    mpath2 (360060e8005491000000049100000700a) dm-1 HP,OPEN-V
>    [size=10G][features=1 queue_if_no_path][hwhandler=0][rw]
>    \_ round-robin 0 [prio=2][active]
>     \_ 3:0:0:1 sdc 8:32  [active][ready]
>     \_ 4:0:0:1 sde 8:64  [active][ready]
>    mpath1 (360060e80054910000000491000007003) dm-0 HP,OPEN-V
>    [size=10G][features=1 queue_if_no_path][hwhandler=0][rw]
>    \_ round-robin 0 [prio=2][active]
>     \_ 3:0:0:0 sdb 8:16  [active][ready]
>     \_ 4:0:0:0 sdd 8:48  [active][ready]
> 
>            If I run multipathd -k and do show config, there is a lot of out
>    put but I think the key things are:
> 
>    defaults {
>            verbosity 2
>            polling_interval 10
>            path_grouping_policy multibus
>            failback 5
>            rr_min_io 10
>            no_path_retry 5
>            user_friendly_names yes
>            bindings_file /etc/multipath.bindings
>    }
> 
>    devices {
>            LOTS OF DEVICE ENTRIES.
> 
>            device {
>                    vendor (HITACHI|HP)
>                    product OPEN-.*
>                    path_checker tur
>                    failback immediate
>                    no_path_retry 12
>                    rr_min_io 1000
>            }
>    }
> 
>            The device entry for the SAN has rr_min_io set to 1000. I added
>    rr_min_io 10 in the default, but per the man page for multipath.conf
>    entries in the defaults will only be used if they do not appear other
>    places.
> 
>    Q1) If I want to over ride the rr_min_io value in the devices/device
>    section can I just add a devices/device section in /etc./multipath.conf
>    with the things I want to change or do I have to duplicate everything that
>    is in the built-in devices/device entry?

I have seen some values not specified in the multipath.conf
devices/device section are picked up from the "default" table (don't
remember if this was internal default table or config default table)
instead of "controller table" (aka built-in devices/device entry
values).  So, the best is to duplicate everything from the internal
controller table.

>    Q2) How can I determine the best value for rr_min_io?
>            I assume whom ever added the HITACHI|HP devices/device built-in
>    entry decide on the value
>            of 1000 for a reason. Maybe they did benchmarks or maybe they just
>    copied another entry
>            that was some what like what they needed and changed the vendor
>    and product.

I doubt if they carried out a benchmark, but possible! At one time the
default used to be 1000. I think it is 1 now with request based
multipath.

Thanks, Malahal.


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