Jeff wrote:
>Veritas Filesystem (VxFS) has had snapshots since the early 90s,
>and Solaris 8 picked up snapshot capabilities a year or so ago.
Interesting. I just checked out some on-line info on the
functionality in Solaris 8 (fssnap). It's not totally clear from what
I've seen so far, but it appears that Sun added snapshot functionality
at the block device level rather then at the filesystem level. Can
anybody confirm this impression? My recollection (from a long time
ago) was that Network Appliances did it more at the filesystem level
(although they kind of mashed the two together).
I can see advantages and disadvantages to either approach.
Disk level - Can be used with any filesystem. Possibly even with
applications (say databases) that read/write raw partitions.
Filesystem level - More efficient implementation? Can more easily share
free space pool between active filesystem and collection of
snapshots. User-visible snapshots may be easier to implement.
Might even allow users to create their own snapshots. Lazy man's
CVS anyone...
Can people who mentioned snapshotting in other systems speak to
which way it's implemented and the pros and cons?
>Elizabeth Zwicky wrote a paper called "Torture-testing Backup and
>Archive Programs: Things You Ought to Know But Probably Would
>Rather Not" in 1991 that may be worth re-reading:
>
>http://ftp.at.linuxfromscratch.org/utils/archivers/star/testscripts/zwicky/testdump.doc.html
Yeah, I think I read that paper at one time. As the title suggests, scary.
Bill Bogstad
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