[Cluster-devel] [PATCH] qdiskd: Make multipath issues go away

[Lon Hohberger]

On 07/02/2012 09:55 AM, Fabio M. Di Nitto wrote:
> From: Lon Hohberger <lhh at redhat.com>
> 
> Qdiskd hsitorically has required significant tuning to work around
> delays which occur during multipath failover, overloaded I/O, and LUN
> trespasses in both device-mapper-multipath and EMC PowerPath
> environments.
> 
> This patch goes a very long way towards eliminating false evictions
> when these conditions occur by making qdiskd whine to the other
> cluster members when it detects hung system calls.  When a cluster
> member whines, it indicates the source of the problem (which system
> call is hung), and the act of receiving a whine from a host indicates
> that qdiskd is operational, but that I/O is hung.  Hung I/O is different
> from losing storage entirely (where you get I/O errors).
> 
> Possible problems:
> 
> - Receive queue getting very full, causing messages to become blocked on
> a node where I/O is hung.  1) that would take a very long time, and 2)
> node should get evicted at that point anyway.
> 
> Resolves: rhbz#782900
> 
> this version of the patch is a backport of:
> e2937eb33f224f86904fead08499a6178868ca6a
> 34d2872fb7e60be1594158acaaeb8acd74f78d22
> 
> There is a minor change vs original patch based on how qdiskd
> in RHEL5 handles cman connection. We add an extra call to cman_alive
> in main qdisk_loop to make sure data are not stalled on the
> cman port, and data_callback to qdiskd_whine executed.
> 
> Signed-off-by: Lon Hohberger <lhh at redhat.com>
> Signed-off-by: Fabio M. Di Nitto <fdinitto at redhat.com>

Re-ack :)