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From: douglis@ginger.Berkeley.EDU (Fred Douglis)
Newsgroups: comp.os.research
Subject: optical disks
Message-ID: <4177@sdcsvax.UCSD.EDU>
Date: Tue, 27-Oct-87 13:11:51 EST
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Posted: Tue Oct 27 13:11:51 1987
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[This is in response to a request for information on optical disks and
Sprite; I thought it might be of interest to the general community,
and I'd be interested in comments. - FD (as opposed to DL)]

Sorry, I haven't written anything on the Sprite archiving system yet
-- I'm only just starting to shift the emphasis of my research toward
optical disks.

I can't tell you too much about disk availability, but I know a
little.  Over the summer at DEC WRL I used Maxtor 800-S drives,
400MB/side, double-sided, cost $1500 each directly from the
manufacturer.  Here at UCB, we apparently couldn't get them from
Maxtor, so we got them from a company called "Corel" in Ottawa --
don't know the cost.  Same drives, though.  We just got them last week
and have not yet hooked them into Sprite.

I understand people elsewhere are using or have ordered drives from
Optimem, as well as Sony and other Japanese firms.  Don't know the
cost.  It seems clear that in the long run, for a centralized archive
service you need a jukebox with many disks rather than a small number
of scattered small drives; however, Hugh Lauer (of Apollo) mentioned
that he thinks it'll be a while before jukeboxes work well enough to
use and thinks instead that people should get large numbers of small
optical disk drives, such as one per workstation plus a few more for
general use.

Cosmos, with its immmutable objects, would be a natural place to use
optical disks, although I worry a bit about storage space: if *every*
past version of *every* object is available, that's a lot of space.
Lot's of people talk about writing out to an optical disk only if a
file survives past a certain lifetime, and that may be the way
we'll go in Sprite -- however, it means that there may be gaps in the
versions in the archive.  Another issue is to distinguish which files
have every version written, and to write every version of things like
C files but not to write out the binaries.  Do you know what you'll be
doing about this?

- Fred -			douglis@ginger.Berkeley.EDU
				ucbvax!douglis