On Mar 19, 2013, at 9:46 PM, NeilBrown wrote:

On Tue, 19 Mar 2013 16:15:35 -0500 Brassow Jonathan [off-list ref]
wrote:

quoted

On Mar 17, 2013, at 6:49 PM, NeilBrown wrote:

quoted

On Wed, 13 Mar 2013 12:29:24 -0500 Jonathan Brassow [off-list ref]
wrote:

quoted

Neil,

I've noticed that when too many devices fail in a RAID arrary that
addtional I/O will hang, yielding an endless supply of:
Mar 12 11:52:53 bp-01 kernel: Buffer I/O error on device md1, logical block 3
Mar 12 11:52:53 bp-01 kernel: lost page write due to I/O error on md1
Mar 12 11:52:53 bp-01 kernel: sector=800 i=3           (null)           (null)  
       (null)           (null) 1

This is the third report in as many weeks that mentions that WARN_ON.
The first two where quite different causes.
I think this one is the same as the first one, which means it would be fixed
by  
    md/raid5: schedule_construction should abort if nothing to do.

which is commit 29d90fa2adbdd9f in linux-next.

Sorry, I don't see this commit in linux-next:
(the "for-next" branch of) git://github.com/neilbrown/linux.git
or git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git

Where should I be looking?

Sorry, I probably messed up.
I meant this commit:
http://git.neil.brown.name/?p=md.git;a=commitdiff;h=ce7d363aaf1e28be8406a2976220944ca487e8ca

Yes, I found this patch in 'for-next'.  I tested 3.9.0-rc3 with and without this patch.  The good news is that my issue with RAID5 appears to be fixed with this patch.  To test, I simply created a 1GB RAID array, let it sync, killed all of the devices and then issued a 40M write request (4M block size).  Before the patch, I would see the kernel warnings and it would take 7+ minutes to finish the 40M write.  After the patch, I don't see the kernel warnings or call traces and it takes < 1 sec to finish the 40M write.  That's good.  Will this patch make it back to 3.[78]?

However, I also found that RAID1 can take 2.5 min to perform the write and RAID10 can take 9+ min.  Hung task messages with call traces and many many errors are the result.  This is bad.  I haven't figured out why these are so slow yet.

On a different topic, I've noticed the following commits in 'for-next':
  90584fc MD: Prevent sysfs operations on uninitialized kobjects
  e3620a3 MD RAID5: Avoid accessing gendisk or queue structs when not available
but these are not in 3.9.0-rc3.  They should make their way into 3.9.0 as well as 3.8.0.  (They apply cleanly to the 3.8 kernel, but I hadn't bothered to notify 'stable' - only mention the regression was introduced in 3.8-rc1.)

Thanks,
 brassow