snapshot implementation

[Bob Friesenhahn]

On Wed, 23 Dec 2009, Patrick Proniewski wrote:

> By the way, I'm also interested in ZFS: is the snapshot technology 
> available in ZFS the same as the one available in UFS?

I don't know anything about snapshots in UFS, but snapshots in ZFS are 
certainly remarkably different.  ZFS uses copy-on-write (COW) whenever 
a data block is updated and snapshot creation simply adds a new 
reference to existing blocks.  The snapshot is made available as a 
(usually) hidden directory (/filesystem/.zfs/snapshot/snapname) which 
contains the complete filesystem content at the time the snapshot was 
taken.  In my experience, ZFS snapshots usually take less than a 
second to complete.  They are so efficient that some systems have 
snapshots scheduled to be taken every five minutes as a defense 
against user/application error.

Bob
--
Bob Friesenhahn
bfriesen at simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/