Date: Mon, 17 Jul 2000 11:15:39 +1000 From: Peter Jeremy <peter.jeremy@alcatel.com.au> To: Kirk McKusick <mckusick@mckusick.com> Cc: arch@FreeBSD.ORG Subject: Re: Snapshots in the Fast Filesystem Message-ID: <00Jul17.111555est.115264@border.alcanet.com.au> In-Reply-To: <200007060342.UAA23667@beastie.mckusick.com>; from mckusick@mckusick.com on Wed, Jul 05, 2000 at 08:42:18PM -0700 References: <200007060342.UAA23667@beastie.mckusick.com>
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On 2000-Jul-05 20:42:18 -0700, Kirk McKusick <mckusick@mckusick.com> wrote: >I have completed an initial implementation of snapshots for the >fast filesystem (UFS/FFS). Thank you very much. Having used the snapshot mechanisms in Compaq's AdvFS, I can say that this will be wonderful. Having read the README that you committed, I have a few questions: Disk space overheads: Does creating a snapshot require any additional disk space? I realize that updates will require additional space for the `before' image, but what other metadata overheads are there? Running out of space: Is there any special behaviour when an active FS with one or more snaphsots runs out of disk space? Does the (oldest?) snapshot become invalid to free up space, or is the behaviour indistinguishable from running out of space without snapshots? How does this interact with the UFS minfree boundary? Speed: Is it possible to reduce the time during which FS activity is suspended? As you point out, one use for snapshots is doing point-in- time backups (I do this currently with Compaq Tru64 AdvFS filesystems). From past experience, I've found that Oracle is very sensitive to FS activity blocks - after about 1 sec, Oracle will abort if it's FS activity is blocked. It's possible that other applications have similar behaviour. Peter To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-arch" in the body of the message
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