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SubjectRe: File system snapshopts: how valuable?
Date
anders.qvist@netg.se writes ("Re: File system snapshopts: how valuable?"):
> Colin Plumb wrote:
>
> > I'm designing another file system, and I've stolen a lot of ideas from
> > Netowrk Appliances' WAFL (write anywhere file layout)

> Very valuable, yes, but to a rather small audience.

I don't think the audience is all that small. Backup tapes are great
for recovering entire filesystems, but they are too slow for
recovering one or two files for just one user. If the filesystem could
automatically maintain snapshots users' files on-line, then you've
saved yourself a lot of time and hastle. Also, users' files are more
likely to be in snapshots than on backup tapes because snapshots are
usaully made quite often (~hourly) and kept for weeks.

> I presume (not knowing a
> lot aboutWAFL and such) that there are rollback/commit-style calls you can
> make to "fix" newly written data in ways similar to what relational databases
> usually do.

For home directories, you make the snapshots automatically, and then
users can access files by looking in ~/.snapshot/ - users don't even
need any special tools.

Another nice feature of the NetApp FAServer is the fact that, modulo
filesystem bugs, it does not need fscking. A new filesystem design
ought to have this feature since fsck would take quite some time to
run on a 50Gb disk.

Peter

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