Snapshot problems

[Xin LI]

On Sun, Jun 26, 2005 at 01:20:31PM -0500, Skylar Thompson wrote:
> I've discovered a repeatable problem with FreeBSD's UFS2 snapshots. If I
> create several snapshots, and then do heavy disk I/O on the original
> filesystem (deletions, creations, simple touches, etc.) I can cause the I/O
> system to crash. There is no kernel panic, and the machine still answers
> pings, but no disk I/O occurs. I can replicate this on a dual-processor
> beige-box system with a Mylex RAID controller and a RAID-5 set, and also on
> a dual-processor Dell Poweredge 2650 with a PERC 3/i RAID controller and a
> RAID-5 set and RAID-1 set.  FreeBSD 5.4-RELEASE is installed on both
> systems, and SMP is enabled as well, with HTT disabled on the Poweredge. I
> have DDB compiled in, so I can get debug information but I don't know what
> to look for.

I think a script that can reliably trigger the "crash" would be helpful.
What do you mean by "IO system crash", BTW?  I got confused since it does
not cause kernel panic and stop ping responses.  Do you mean that the
I/O system was stalled/suspended when there is heavy disk operations?

My guess is that there is some underlying deadlock(s) present.  Would you
mind compiling WITESS/WITESS_SUPPORT into your kernel and give it a try?
This will reduce performance, but would also be helpful for picking locking
bugs.

Thanks in advance!

Cheers,
-- 
Xin LI <delphij frontfree net>	http://www.delphij.net/
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