[dm-devel] General and configuration questions

Allen, Jack Jack.Allen at mckesson.com
Fri May 28 21:16:34 UTC 2010


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?

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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