Allen, Jack [Jack.Allen@xxxxxxxxxxxx] 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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