On Jun 15, 2011, at 4:45 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.
ouch > > I suspect rather than that it is more that Richard equated "write" to > write(2) / dmu_write() calls and that would suck performance wise. Yep, especially because you also have to write the metadata that said when you wrote, and so on. > > 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() ]. > >> 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. Yes, and as others have said, the appropriate interface is critical. A WebDAV PUT does have a bounded endpoint where version control makes sense. An mmap(2) does not. Adding a call to zfs snapshot when a WedDAV PUT completes seems trivial. But you could also call a traditional source code control system check-in as well. Before long, you can have a useful CMS system. There are a large number of programs that are designed to not close files, and it will be difficult to derive meaningful snapshot opportunities in those cases. > 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. > If you move further down then doing a snapshot on every dmu_write() call is > fundamentally at odds with how ZFS works. Yep. -- richard _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
