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From: terryl@tekcrl.LABS.TEK.COM
Newsgroups: comp.periphs
Subject: Re: WORMs acting like R/W disks...
Message-ID: <4565@tekcrl.LABS.TEK.COM>
Date: 25 Aug 89 18:17:03 GMT
References: <680@rna.UUCP> <191@arnor.UUCP> <683@rna.UUCP> <423@siswat.UUCP>
Reply-To: terryl@tekcrl.LABS.TEK.COM
Organization: Tektronix, Inc., Beaverton,  OR.
Lines: 51

In article <423@siswat.UUCP> buck@siswat.UUCP (A. Lester Buck) writes:
+> In article <191@arnor.UUCP> uri@arnor.UUCP (Uri Blumenthal) writes:
+> >From article <680@rna.UUCP>, by dan@rna.UUCP (Dan Ts'o):
+> >> ......makes the WORM emulate a read/write
+> 	Well, of course it wouldn't be very good for putting your
+> /usr/spool/news filesystem on. But /usr/src, probably pretty good. The point
+> is that many of us have storage applications requiring random, moderately fast
+> access (scratch Exabyte), large capacity and not too many changes (images,
+> for example, or school records), but have not been able to use WORMS
+> effectively because existing OS's and device drivers and filesystems require
+> read-write semantics. Special software drivers must be written to allow
+> transparent access to WORMS from UNIX, MSDOS, VMS, etc. However this OCU
+> box eliminates the need for special software by putting all those functions
+> and workarounds in "hardware" (host and OS independent hardware).
+> 	But the write-once limitation isn't going to go away, not entirely.
+> Sometimes you want 800Mb of archival info on a $100 cartridge.
+
+If you really want to know how to make a WORM look like a magnetic disk,
+get a copy of the Summer '88 Usenix paper, "A UNIX File System for a
+Write-Once Optical Disk", by Terry Laskodi et al. at Tektronix.
+This is a filesystem built inside a Unix device driver which presents
+a read/write disk to the operating system (though, of course, with lots
+of writing the free space declines).  It is based on the report
+"An Efficient I/O Interface for Optical Disks" by Jeffrey Scott Vitter,
+Tech Report No. CS-84-15, June 1984, CS Dept, Brown University, where
+Vitter presents some data structures for using WORMs and proves that
+these algorithms are optimal (under some assumptions).


<Enter gratuitous back slapping mode, for the second time in as many months..>

     If you can't find a copy of my paper that Mr. Buck refers to, send me
a SNAIL-MAIL address (NO EMAILS!!! The paper is NOT in a form that is suitable
for email delivery), and I'll send you a copy of the paper. NOTE: the software
described is NOT available for distribution, although it shouldn't be too
difficult to reproduce....

				Terry Laskodi
				     of
				Tektronix


	    terryl@tekcrl.labs.tek.com	(If your mailer groks domains)

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