On 15/06/11 7:45 AM, Darren J Moffat wrote: > On 06/15/11 12:29, Edward Ned Harvey wrote: >>> From: zfs-discuss-boun...@opensolaris.org [mailto:zfs-discuss- >>> boun...@opensolaris.org] On Behalf Of Richard Elling >>> >>> That would suck worse. >> >> Don't mind Richard. He is of the mind that ZFS is perfect for everything >> just the way it is, and anybody who wants anything different should >> adjust >> their thought process. > > I suspect rather than that it is more that Richard equated "write" to > write(2) / dmu_write() calls and that would suck performance wise. > > I also suspect that what Simon wants isn't a snapshot of every little > write(2) level call but when the file is completed being updated, maybe > on close(2) [ but that assumes the app does actually call close() ]. >
That's how I interpreted it. >> I know I've certainly had many situations where people wanted to >> snapshot or >> rev individual files everytime they're modified. As I said - perfect >> example is Google Docs. Yes it is useful. But no, it's not what ZFS >> does. > > Exactly versions of a whole file, but that is different to a snapshot on > every write. > > How you interpret "on every write" depends on where in the stack you are > coming from. If you think about an application a "write" is whey you > save the document but at the ZPL layer that is multiple write(2) calls > and maybe even some rename(2)/unlink(2)/close(2) calls as well. That's one big problem with the naive plan of using snapshots. Another one is that snapshots are per-filesystem, while the intention here is to capture a document in one user session. Taking a snapshot will of course say nothing about the state of other user sessions. Any document in the process of being saved by another user, for example, will be corrupt. The proposal seems to be aimed at the wrong part of the stack. The comparison with Google Docs is revealing. --Toby > If you move further down then doing a snapshot on every dmu_write() call > is fundamentally at odds with how ZFS works. > _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
