mksnap_ffs takes 4-5 minutes?

[Chris Dillon]

On Fri, 22 Jul 2005, Eric Anderson wrote:

> The snap seemed to suspend the filesystem nearly immediately, and 
> kept it suspended for quite some time - I would say probably more 
> than half the time. In order for snapshots to be very useful, it 
> must work on large filesystems (100GB+) in a reasonable amount of 
> time (a few seconds would be ok).  I know for certain that one test 
> filesystem (2Tb) had nothing on it, no processess using the 
> filesystem at all, and it took well over an hour to run mksnap on 
> it.

Just another datapoint -- I take daily snapshots of a 270GB filesystem 
and it takes 3 to 4 minutes (not sure down to the second).  I used to 
take multiple snapshots during the day but suspending the filesystem 
for several minutes at peak times wasn't working out (and seemed to 
cause complete system hangs, sometimes), so I just went to once per 
day during off-hours.  Making the snapshots seems to be mostly I/O 
bound, and this is on a system with a fairly fast RAID5 array of 
10KRPM SCSI drives.  The suspension of the filesystem also seems 
immediate to me, so it seems most of the time is actually spent making 
the snapshot.

Filesystem          1K-blocks     Used     Avail Capacity iused   ifree %iused  Mounted on
/dev/da1s1a         272092768 16863968 233461380     7%  155146 8435700    2%   /userspace

Jul 20 00:14:11 rshome root: snapshot: daily.0 snapshot on filesystem /userspace made (duration: 4 min)
Jul 21 00:14:01 rshome root: snapshot: daily.0 snapshot on filesystem /userspace made (duration: 3 min)
Jul 22 00:14:04 rshome root: snapshot: daily.0 snapshot on filesystem /userspace made (duration: 4 min)

I'm using Ralf S. Engelschall's snapshot management scripts, though I 
know that has no effect on the time it takes to create a snapshot.


-- 
  Chris Dillon - cdillon(at)wolves.k12.mo.us
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