Snapshot problems

[Chris Dillon]

On Sun, 26 Jun 2005, 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 see a similar problem (I think stuck processes show they are in the 
'disk wait' state in top/ps), but my problem occurs on a production 
box so I've been unable to debug it.  I've taken to rebooting the box 
automatically every day about 15 minutes before the snapshots are 
scheduled to be made using Ralf S. Engelschall's snapshot scripts 
(http://people.freebsd.org/~rse/snapshot/). The daily reboot seems to 
prevent the problem from happening.  If I don't reboot the system 
daily, I can only go one to three days without a problem.

> 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'm using FreeBSD 5.4-STABLE on a relatively new dual-processor HP 
DL380 G3 with integrated SmartArray 5i+ and a 7-disk RAID5 array. 
Given the range of hardware we are seeing the problem on, it doesn't 
seem to be hardware or driver related.

In the meantime, try rebooting the box at a scheduled time every day 
to see if that helps alleviate your problem.

-- 
  Chris Dillon - cdillon(at)wolves.k12.mo.us
  FreeBSD: The fastest, most open, and most stable OS on the planet
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