Date: Wed, 23 Dec 2009 10:41:34 -0600 (CST) From: Bob Friesenhahn <bfriesen@simple.dallas.tx.us> To: Patrick Proniewski <patpro@patpro.net> Cc: freebsd-fs@freebsd.org Subject: Re: snapshot implementation Message-ID: <alpine.GSO.2.01.0912231031450.1586@freddy.simplesystems.org> In-Reply-To: <32CA2B73-3412-49DD-9401-4773CC73BED0@patpro.net> References: <32CA2B73-3412-49DD-9401-4773CC73BED0@patpro.net>
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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@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/ GraphicsMagick Maintainer, http://www.GraphicsMagick.org/
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