panic: ffs_valloc: dup alloc

[Uwe Doering]

Eric Anderson wrote:
> I get the above panic after nfs clients attach to this nfs server and 
> being read/write ops on it after an unclean shutdown.  I've fsck'ed the 
> fs, and it marks it as clean, but I get this every time.  It's an NFS 
> share of a GEOM stripe (about 2TB).
> mode = 0100600, inum = 58456203, fs = /mnt
> panic: ffs_valloc: dup alloc

Do you happen to have disk mirroring on this server (RAID 1)?  At work, 
on a workstation with RAID 1, we once had a case where after a power 
failure fsck would succeed, but subsequently, when mounting and using 
the partitions, the kernel still paniced because of a corrupt 
filesystem.  Repeatedly.

This caused some major head scratching on our part until we figured out 
what was happening.  The mirrored disks had gone out of sync.  For 
performance reasons, a RAID 1 controller reads data from one disk drive 
or the other, depending on which drive is less busy in that particular 
moment.  So while fsck was able to find and fix some filesystem 
inconsistencies there were still some more left in disk sectors it 
didn't access.

The RAID controller we used turned out to have a verification mode where 
it would scan the disks and re-synchronize them.  Afterwards we did 
another fsck run, and this fixed the remaining filesystem 
inconsistencies.  The kernel panics were gone.

Now, with the information you've provided I can't tell whether these 
findings apply to your case, but perhaps this story helps at least 
others in a similar situation.

    Uwe
-- 
Uwe Doering         |  EscapeBox - Managed On-Demand UNIX Servers
gemini at geminix.org  |  http://www.escapebox.net