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() ].
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.
If you move further down then doing a snapshot on every dmu_write() call
is fundamentally at odds with how ZFS works.
--
Darren J Moffat
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