[dm-devel] boot scripts and dm-multipath

[Edward Goggin <egoggin emc com>]

Resending this since I think I got no feedback last time.

Linux distributions currently invoke /sbin/multipath fairly early in the
boot sequence, followed sometime later by /sbin/multipathd.  I think
that these distributions run the risk of incurring a boot-time hang
when/if read I/Os issued (by kpartx in /etc/boot.multipath for instance)
to dm-multipath devices before multipathd is started, fail (due to
failures which are not SCSI transport related) when sent to storage
targets configured with the dm-multipath queue_if_no_path feature.
Without multipathd running there is no ability to timeout the "queue I/O
forever" behavior during an all-paths-down use case.

In these cases, the dm-multipath device is created because the storage
target responds successfully to the device id inquiry request for each
path but all path tests and read/write I/O requests issued on all paths
to the device will fail.  If the dm-multipath device was configured with
the queue_if_no_path feature, the kernel dm-multipath code will queue
the failed read/write I/O indefinitely.

Newer versions of multipathd (that is, ones based on
multipath-tools-0.4.7) do not need to invoke multipath in order to
configure the dm-multipath, simply invoking multipathd suffices.  Is it
reasonable to change these scripts to invoke multipathd instead of
multipath at early boot and not invoke multipath at all from these
scripts?