mksnap_ffs time

Eric Anderson anderson at
Thu Jan 3 18:32:35 PST 2008

On 01/03/08 17:46, Daan Vreeken [PA4DAN] wrote:
> On Friday 04 January 2008 00:30:20 you wrote:
>> Hi!
>>> 1) Is anyone else seeing this?
>> As far as I know, this is somehow related to the SoftUpdates, but I am not
>> 100% sure. Look at the mailinglist archives, there was a discussion a few
>> months ago about the same topic as far as I remember.
>> Please note that according to
>> a filesystem can only have 20 snapshots! :-)
> Hmm.. Then at least time spent per snapshot isn't going to get much worse than 
> it is today ;-)
> Too bad this limitation isn't mentioned in 'man 8 mksnap_ffs'. If this 
> limitation is still there, I think it deserves a place in the manual.

The limitation is still there, and probably should be mentioned in the 
manual - good point.

The time is spent making copies of all the cylinder groups, which there 
are a *lot* of on a 700GB file system.  When UFS snapshots were 
developed, 4-20GB file systems were pretty big.  Over time, this problem 
is going to just get worse.  :(

The only way to help it, is to use some custom newfs options to reduce 
the number of cylinder groups, but it won't buy you much.

Snapshots also impede on your general file system performance.  In 
FreeBSD 7, you could use ZFS, which would give you the power and control 
you need (plus FreeBSD 7 has many many performance improvements).


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