Date: Fri, 25 Dec 2009 15:29:53 +0100 From: patpro <patpro@patpro.net> To: Barry Pederson <bp@barryp.org> Cc: freebsd-fs@freebsd.org Subject: Re: snapshot implementation Message-ID: <3ea87f5f62bb8ba30d798d4605a64c83@localhost> In-Reply-To: <4B3283F2.7060804@barryp.org> References: <32CA2B73-3412-49DD-9401-4773CC73BED0@patpro.net> <alpine.GSO.2.01.0912231031450.1586@freddy.simplesystems.org> <4B3283F2.7060804@barryp.org>
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On Wed, 23 Dec 2009 14:56:18 -0600, Barry Pederson <bp@barryp.org> wrote: > "...there's virtually no overhead at all due to the copy-on-write > architecture. In fact, sometimes it is faster to take a snapshot rather > than free the blocks containing the old data!" > > That's certainly not the case with UFS snapshots, which can take a long > time to complete (we're talking freezing your machine's disk activity > for many minutes), and are limited to 20 total. UFS uses copy on write. But you say many minutes to complete? Don't you speak about dump(1), that uses snapshot as a basis to dump a live file system? I agree, UFS snapshot creation is not lightning-fast, but many minutes seems a lot to me, and I never experienced such a long creation time. patpro
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