RHEL 6.4, Yes I know it's old. I have no choice.
According to the multipath.conf man page, the default grouping policy is multibus. That is, multipaths should be shown as follows:
# multipath -ll mpathc (360002ac0000000000000086c00002ce2) dm-0 3PARdata,VV size=16G features='0' hwhandler='0' wp=rw `-+- policy='round-robin 0' prio=1 status=active |- 2:0:0:0 sdd 8:48 active ready running |- 3:0:0:0 sde 8:64 active ready running |- 3:0:1:0 sdf 8:80 active ready running `- 2:0:1:0 sdg 8:96 active ready running
There is a single group with four paths in it. Multibus. So far so good.
Now, when connecting to an iSCSI target, I get a failover configuration. I swear the multipath.conf file contains nothing about the grouping policy, so that I expect a default multibus grouping:
# multipath -v2 create: rusty13lun1 (1201311201301) undef L-and-D,Spinning Rust size=16G features='0' hwhandler='0' wp=undef |-+- policy='round-robin 0' prio=1 status=undef | `- 4:0:0:1 sdh 8:112 undef ready running `-+- policy='round-robin 0' prio=1 status=undef `- 5:0:0:1 sdl 8:176 undef ready running
There is one group per path. Failover.
When explicitly requesting multibus for the iSCSI LUN, a multibus configuration is created as expected.
I double checked this with dmsetup (sorry, I didn't save the output).
My questions: Is multibus really the default? What might make dmsetup or multipathing choose a certain policy?
This is on a training system that I currently don't have access to, so that I can't investigate any further unfortunately.