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
>
>
>
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