[dm-devel] Multipath not balancing I/O across paths evenly.

[Devin]

We started to notice that on our iSCSI hosts that are using Multipath that
they seem to be sending most of the traffic across one port even though
they have 4 paths for each mpath device. We are using a Hitachi SAN.

Here is my multipath configuration:
defaults {
        user_friendly_names yes
}

devices {
        device {
                vendor                   "HITACHI"
                product                  "DF.*"
                path_grouping_policy  multibus
                path_checker              tur
                getuid_callout            "/sbin/scsi_id -g -u -s /block/%n"
                no_path_retry             1
                features                  "1 queue_if_no_path"
                }
}


The output of multipath looks like:

mpath2 (360060e80101af190058baee900000007) dm-6 HITACHI,DF600F
size=1.5T features='1 queue_if_no_path' hwhandler='0' wp=rw
`-+- policy='round-robin 0' prio=0 status=active
  |- 8:0:0:1   sdg  8:96   active ready running
  |- 9:0:0:1   sdh  8:112  active ready running
  |- 7:0:0:1   sdf  8:80   active ready running
  `- 10:0:0:1  sdi  8:128  active ready running
mpath0 (360060e80101af190058baee900000005) dm-5 HITACHI,DF600F
size=1.0T features='1 queue_if_no_path' hwhandler='0' wp=rw
`-+- policy='round-robin 0' prio=0 status=active
  |- 9:0:0:0   sdd  8:48   active ready running
  |- 8:0:0:0   sdc  8:32   active ready running
  |- 10:0:0:0  sde  8:64   active ready running
  `- 7:0:0:0   sdb  8:16   active ready running

However when I do a tcpdump and count the number of packets to each of the
IQN's they are not equal, not even close.


IQN1: 19,579

IQN2: 12,778

IQN3: 70,674

IQN4: 67


Is there anything I need to do in order to ensure that Multipath balances
more evenly across all the paths???

Any help would be appreciated.


Devin
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