BOFH Hunter

dm-multipath and the ds4700

For around a year now, I’ve been wanting to move away from IBM’s (okay, LSI’s) rdac mpp drivers used for the ds4XXX  series disk chassis on RHEL and CentOS. When RHEL 5.3 came out boasting support dm-multipath support for the DS4XXX series, I was understandably overjoyed. The only problem was I couldn’t make it work. After several rounds of cursing, muttering and poking folks smarter than me to help out, the problem became immediately clear.

The example configs which work fine for the ’supported’ platforms have a text string mismatch when using the ‘unsupported’ ds4700. Basically you have to change a bit of text slightly because the hardware identifies itself slightly differently. Who’d have thunk it, right?

Below is the multipath.conf snippet I’ve been using now for the past month with some pretty good success.


defaults {
user_friendly_names yes
}
blacklist {
devnode "^(ram|raw|loop|fd|md|dm-|sr|scd|st)[0-9]*"
devnode "^(hd|xvd|vd)[a-z]*"
wwid "*"
}
blacklist_exceptions {
wwid "3600XXXX"
}
devices {
device {
vendor "IBM"
product "1814 FAStT"
getuid_callout "/sbin/scsi_id -g -u -s /block/%n"
prio_callout "/sbin/mpath_prio_rdac /dev/%n"
features "0"
hardware_handler "1 rdac"
path_grouping_policy group_by_prio
failback immediate
rr_weight uniform
no_path_retry queue
rr_min_io 1000
path_checker rdac
}


Now clearly you’ll have to modify the wwid to suit your own environment, and you’ll also want to exclude the non-multipath device references (/dev/sdb for example) from lvm.conf if you’re using lvm.  This got things going for me, so hopefully it’ll help others out as well.