running mksnap_ffs

[Kris Kennaway]

On Thu, Jan 11, 2007 at 11:25:34AM -0800, Scott Oertel wrote:
> Kris Kennaway wrote:
> >On Tue, Jan 02, 2007 at 09:06:24PM +0100, Willem Jan Withagen wrote:
> >  
> >>Hi,
> >>
> >>I got the following Filesystem:
> >>Filesystem    Size    Used   Avail Capacity iused     ifree %iused 
> >>/dev/da0a     1.3T    422G    823G    34%  565952 182833470    0%
> >>
> >>Running of a 3ware 9550, on a dual core Opteron 242 with 1Gb.
> >>The system is used as SMB/NFS server for my other systems here.
> >>
> >>I would like to make weekly snapshots, but manually running mksnap_ffs 
> >>freezes access to the disk (I sort of expected that) but the process 
> >>never terminates. So I let is sit overnight, but looking a gstat did not 
> >>reveil any activity what so ever...
> >>The disk was not released, mksnap_ffs could not be terminated.
> >>And things resulted in me rebooting the system.
> >>
> >>So:
> >> - How long should I expect making a snapshot to take:
> >>	5, 15, 30min, 1, 2 hour or even more???
> >>    
> >
> >Yes :) Snapshots were not designed for use in this way (they were
> >designed to support background fsck and allow faster system recovery
> >after power failure), so they don't scale as well as you might like on
> >large filesystems.
> >
> >Kris
> >  
> 
> 
> If snapshots were designed to support background fsck, then why did they 
> not make it more scalable? If you can't create a snapshot without the 
> system locking up, that means fsck won't be able to either, making 
> background fsck worthless for systems with large storage.

locking up != taking a long time to complete.  You haven't
differentiated between those two situations yet.

Kris
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