Date: Fri, 3 Mar 2000 14:49:48 -0800 (PST) From: Brian Beattie <beattie@aracnet.com> To: Michael Bacarella <mbac@bsd4.nyct.net> Cc: Julian Elischer <julian@elischer.org>, David Scheidt <dscheidt@enteract.com>, freebsd-hackers@FreeBSD.ORG Subject: Re: Copy-on-write filesystem Message-ID: <Pine.LNX.4.21.0003031447050.22409-100000@shell1.aracnet.com> In-Reply-To: <Pine.BSF.4.02A.10003031650060.28555-100000@bsd4.nyct.net>
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On Fri, 3 Mar 2000, Michael Bacarella wrote: > > > > It wouldn't be. This is how NetApp do their .snapshot direcotries. I think > > > they have some white papers on it on their website. It's very handy. > > > > Kirk McKusick is implementing a Copy-on write functionality > > for UFS. It is used in conjunction with Soft updates to produce > > snapshots. It's not what you asked for, but still relevant > > I think. One problem with "Copy-on-write, when applied to > > file copies is that you need to assign the blocks up front, even if you > > don't copy the data, as otherwise you could run out of space > > when the copy is actually needed. > > That's the only real drawback I've considered. > > People accept it (barely) when the OS commits to providing virtual memory > it does not have, killing processes when the system falls into debt. > > No one will appreciate that happening to their "permanent" data, > especially if the OS decides that the best way to get out of debt is by > deleting a file :) > Actually, since this is copy-on-write, you do not need the block, until you write. If you need to make a copy, it will be on a write system call (possibly an inode update), just fail the write ENOSPC or whatever. Or am I missing something simple here. > -MB > > > > To Unsubscribe: send mail to majordomo@FreeBSD.org > with "unsubscribe freebsd-hackers" in the body of the message > Brian Beattie | The only problem with beattie@aracnet.com | winning the rat race ... www.aracnet.com/~beattie | in the end you're still a rat To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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