Comment 5 for bug 824790

So the paths not showing up with a config file error, a few well
placed regexp and a proper blacklist to filter out the internal disks
solved that. Also added scsi_dh_rdac to initial ramdisk. Now the paths
are up, and stay up. However when we tried testing failover using
a scsi "delete" of the primary member. The secondary never became
active.

We asked the customer to check with any additional SAN side
config, like automatic lun transfer, is necessary. Depending on how
that turns it we may actually have a real failover bug.

Working multipath config, taken almost verbatim from the IBM
documentation: Section 5-10.
ftp://ftp.software.ibm.com/systems/support/system_x_pdf/94y8402.pdf

# Canonical Customer Support: 08/12/11
# Version 1.2

blacklist {
  devnode "^(ram|raw|loop|fd|md|dm-|sr|scd|st)[0-9]*"
  devnode "^hd[a-z]"
  # Ignore internal storage from the LSI RAID
  device {
    vendor LSILOGIC
    product .*
  }
}

devices {
  device {
    vendor "IBM"
    product ".*"
    path_grouping_policy group_by_prio
    path_checker rdac
    getuid_callout "/lib/udev/scsi_id -g -u -d /dev/%n"
    prio_callout "/sbin/mpath_prio_rdac /dev/%n"
    hardware_handler "1 rdac"
    failback immediate
# rr_weight uniform
    no_path_retry 30
    rr_min_io 100
    features "2 pg_init_retries 50"
  }
}