Snapshot corruption on 6.1/amd64

Eric Anderson anderson at
Thu Sep 21 13:42:58 PDT 2006

On 09/21/06 14:59, James Lauser wrote:
> Hello.
> I've been having some trouble with snapshots on my FreeBSD 6.1/amd64  
> system.  Basically, I have this system set up with a 3ware RAID card  
> and several disks, and use it to collect backups from my other  
> FreeBSD server (sparc64) and three Macs via rsync..
> Every night, I have a script generate a snapshot of the RAID's file  
> system, and those snapshots are kept on the system for one week  
> before being removed (i.e. there are always 7 snapshots present on  
> the system), so I can recover files that were accidentally removed or  
> changed.
> The problem is that when a large number of files are removed or  
> changed on the file system, the corresponding files in the snapshot  
> get corrupted.  This, obviously, makes the snapshots quite useless.
> After some searching, I've found a bug report filed last year that  
> describes this problem exactly, though the log of that report does  
> not suggest that anything has been done with it.  That report is at  
> Any help would be greatly appreciated.  A test I ran showing the  
> problem, plus the output of uname -a and dmesg.boot is attached.
> Thanks in advance.

> Sledge# cd /raid
> Sledge# touch foo
> Sledge# ls -l foo
> -rw-r--r--  1 root  wheel  0 Sep 18 14:07 foo
> Sledge# mksnap_ffs /raid /raid/.snap/snap
> Sledge# rm foo
> Sledge# mdconfig -a -t vnode -f /raid/.snap/snap -u 4
> WARNING: opening backing store: /raid/.snap/snap readonly
> Sledge# mount -r /dev/md4 /mnt
> Sledge# cd /mnt
> Sledge# ls -l foo
> ls: foo: Bad file descriptor
> Sledge# 
> Sledge# 
> Sledge# 
> Sledge# uname -a
> FreeBSD 6.1-RELEASE-p6 FreeBSD 6.1-RELEASE-p6 #4: Wed Sep  6 23:30:56 EDT 2006     root at  amd64

Hmm.. Interesting, it seems to work fine for me:

[root at neutrino /tmp]# dd if=/dev/zero of=TESTDISK bs=1m count=100
100+0 records in
100+0 records out
104857600 bytes transferred in 3.390829 secs (30923882 bytes/sec)
[root at neutrino /tmp]# mdconfig -a -t vnode -f ./TESTDISK
[root at neutrino /tmp]# newfs -U /dev/md0
/dev/md0: 100.0MB (204800 sectors) block size 16384, fragment size 2048
         using 4 cylinder groups of 25.02MB, 1601 blks, 3264 inodes.
         with soft updates
super-block backups (for fsck -b #) at:
  160, 51392, 102624, 153856
[root at neutrino /tmp]# mount /dev/md0 /mnt
[root at neutrino /tmp]# touch /mnt/foo
[root at neutrino /tmp]# mksnap_ffs /mnt/ /mnt/.snap/snap
[root at neutrino /tmp]# mdconfig -a -t vnode -f /mnt/.snap/snap
WARNING: opening backing store: /mnt/.snap/snap readonly
[root at neutrino /tmp]# mount -r /dev/md1 /mnt2
[root at neutrino /tmp]# cd /mnt2
[root at neutrino /mnt2]# ls -l foo
-rw-r--r--  1 root  wheel  0 Sep 21 15:37 foo
[root at neutrino /mnt2]#

Can you unmount /raid, and do an fsck -y /raid and make sure it's clean? 
Also - are you using quotas?  How big is the filesystem?


Eric Anderson        Sr. Systems Administrator        Centaur Technology
Anything that works is better than anything that doesn't.

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