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[dm-devel] General and configuration questions

Title: General and configuration questions

        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 {

        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?

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 am sure I will have more questions depending on the answers I get to these questions.

Jack Allen

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