[linux-lvm] exception when snapshot size is less than the volume size

[Sagar Borikar]

Hi Milan,
   
  Thanks a lot!
  It worked very nice!
   
  Cheers
  Sagar

Milan Broz <mbroz at redhat.com> wrote:
  Hi,

this is an old snapshot bug, already fixed in all
recent kernels - see http://bugzilla.kernel.org/show_bug.cgi?id=7040

Plese could you try to apply patch mentioned in this bugzilla ?
also here
http://git.kernel.org/?p=linux/kernel/git/stable/linux-2.6.18.y.git;a=commitdiff;h=2b64e22fdbc35b4a0e7c1cbda590daaced401c35;hp=6e28fa8b0390dcbb883994f3c634c1f56fe4f93a

(or simply use latest stable 2.6.18.8 kernel)

Milan
--
mbroz at redhat.com

Sagar Borikar wrote:
> In my NAS box, I observed strange thing yesterday. I had the snapshot
> size (32MB) less than volume size was (10 GB) You can say I was trying
> to do failure analysis of my box. The LVM HOwto for snapshot says
> "
> **
> 
> 
> If the snapshot logical volume becomes full it will be dropped (become
> unusable) so it is vitally important to allocate enough space. The
> amount of space necessary is dependent on the usage of the snapshot, so
> there is no set recipe to follow for this. If the snapshot size equals
> the origin size, it will never overflow.
> 
> "
> But my box was crashed in this scenario.
> Was wondering why didn't it disable the snapshots. 
> The underlying processor is MIPS and linux kernel version is 2.6.18.
> After delving little bit in the sources I found that break is occurring
> while blowing away the snapshot facility -- so it`s not surprising that
> snapshots do not work anymore. Just before the error,
> kcopyd_client_destroy is called -- so that`s it for kcopyd jobs -- hence
> snapshots. The snapshot faciltiy is gone at that point, with or without
> the BUG_ON. The error actually occurs while freeing the exception tables
> in the slab cache.
> 
> Any pointers if this has been resolved?
> I am working with lvm version 2.02.28. and device mapper version 1.02.22

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