Repository on LVM filesystem snapshot

[Lasse Kliemann]

Under Linux, LVM allows to take a snapshot of a filesystem.  
(Solaris had a similar feature for years.) This is used in order 
to take a backup (with rsync, tar, etc.) reflecting the 
filesystem's state at a particular time. AFAIK there is no other 
way to get that on a live filesystem.

Although the snapshot is consistent in that respect that it does 
reflect a state of the filesystem at a point of time, this does 
not mean that is is also consistent from the viewpoint of 
applications. For instance, suppose there is a Mercurial 
repository on the filesystem, and the snapshot is taken during a 
transaction or similar. Then the original filesystem is lost 
(say, due to hardware failure) and the admin restores it using a 
copy taken from the snapshot. Is it guaranteed that this gives 
again a fully-functional repository?

I think it should, since the transaction might also be interupted 
for a lot of other reasons.
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