File system snapshopts: how valuable?

Colin Plumb (colin@nyx.net)
Sat, 14 Mar 1998 14:18:07 -0700 (MST)


I'm designing another file system, and I've stolen a lot of ideas from
Netowrk Appliances' WAFL (write anywhere file layout), which you can
see all about at http://www.netapp.com/technology/level3/3002.html.

One feature they have which is rather cool, is snapshots: they
can take a static copy of the file system at any time and keep it
on line as a backup. Further writes are done via COW techniques;
new data is written to new blocks and the old data is preserved.

The only problem is that this complicates things like memory-mapped
files (which NetApp's NFS server doesn't have to worry about).
I'm wondering whether it's a valuable feature worth trying to
implement or not.

I suppose big-linux would be a better place to ask, but does anyone here
have any opinions? If it were free, obviously I'd put it in, but
there's significant hassle involved in some of the bookkeeping.

-- 
	-Colin

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