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From: romkey@ASYLUM.SF.CA.US (John Romkey)
Newsgroups: comp.protocols.tcp-ip.ibmpc
Subject: RVD (was: PD PC-NFS)
Message-ID: <9010151113.AA00991@asylum.sf.ca.us>
Date: 15 Oct 90 18:13:49 GMT
References: <2920@jaytee.East.Sun.COM>
Sender: daemon@ucbvax.BERKELEY.EDU
Reply-To: romkey@asylum.sf.ca.us
Organization: The Internet
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Yes, Geoff is right about RVD. It was actually originally done to
allow LCS to have its many VAX 750's (each complete with about 28MB of
disk) to share filesystems on a disk server. Each fileserver had
several RA81's, later to be replaced by Fujitsu Eagles, which had a
lower failure rate (the 6 RA81's were replaced about 14 times in 12
months - this was quite a few years ago).

RVD actually dedicated entire UNIX partitions of the physical disk to
the server, so you didn't have the extra overheard of going through
the UNIX filesystem. A disk could have multiple readers, one writer or
multiple writers. The idea was that if there were multiple writers
there would be an extra protocol used among the writers to synchronize
them. I don't believe this ever got done.

As a hack, we wrote an RVD driver for DOS. Then people could share a
common DOS filesystem with binaries and things on it, and also have
private ones so it didn't matter if they didn't have a hard drive.
I don't think it ever made it into a public PC/IP distribution, though
several people got private copies. Doing this required some changes to
PC/IP so that you could run both RVD and a PC/IP application (each had
its own linked in driver and protocol stack). It was done by having
some conventions in the code about (1) not accessing the RVD drives
from PC/IP programs and (2) trying to have the PC/IP programs always
leave the network card in the same state they found it in. This was in
the days before we had TCP/IP TSRs.

Anyway, it worked, it was pretty slow, and the model of communication
really was at a disk level, not a filesystem level, so you couldn't
*really* share the filesystem the way you'd like to. I don't know of
anyone who uses RVD now, I don't know where to even find the specs for
it anymore. I'd much rather use NFS myself.
			- john romkey
USENET/UUCP: romkey@asylum.sf.ca.us	Internet: romkey@ftp.com