multipathd and RDAC

J Martin Rushton · 02-04-2015, 08:05 AM

Our cluster was supplied with two IBM DS3400 RAID arrays connected with fibre channel. Both are old and one is failing so we bought an IBM V3700 to replace it. The V3700 complained that we were using the IBM's RDAC driver (true) and we were advised to change to using Linux multipath. I've done that but the default configuration for the DS3400s is:

Quote:

device {
vendor IBM
product 1726-4xx
path_checker rdac
features 1 queue_if_no_path
hardware_handler 1 rdac
prio_callout /sbin/mpath_prio_rdac /dev/%n
no_path_retry 300
rr_min_io 1000
}

The V3700 is still complaining and I note the "path checker rdac" and mpath_prio_rdac lines. Is this rdac the same as IBM's RDAC, and if so how can I get rid of it?

OS is CentOS 5.3 (yes, I know - upgrade), filesystem is GPFS.

smallpond · 02-04-2015, 03:39 PM

rdac was implemented as a standalone driver before being made a plug-in to the dm-multipath driver. Both implement the asymmetric failover used by the LSI (now Netapp) RAID controllers. The stanza from /etc/multipath.conf that you list will match any device where vendor="IBM" and product="1726-4xx" and revision=*. You can see what the values for your V3700 are by doing:

Code:

cat /proc/scsi/scsi

J Martin Rushton · 02-04-2015, 04:08 PM

I'm sorry if I didn't make myself clear. The 1726-4xx is yet another number for the DS3400, the stanza shown I obtained by using:

Code:

# multipathd -k
multipath> show config
...

The relevant stanza for the V3700 was given to me by the suppliers. The V3700 stanza has no rdac mentioned.

When I run the GUI to talk to the V3700 It complains that other controllers (the DS3400s) are using RDAC and the V3700 then refuses to play ball. I'm at home now (it's 22:00 UK time) so will have a further look in the morning.