Path: utzoo!mnetor!uunet!seismo!sundc!pitstop!sun!decwrl!ucbvax!XX.LCS.MIT.EDU!ROMKEY
From: ROMKEY@XX.LCS.MIT.EDU (John Romkey)
Newsgroups: comp.protocols.tcp-ip
Subject: Re: Remote Virtual Disk
Message-ID: <12364793852.14.ROMKEY@XX.LCS.MIT.EDU>
Date: 7 Jan 88 22:41:14 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The ARPA Internet
Lines: 47

A recent message contained some disinformation about RVD.

RVD is the Remote Virtual Disk protocol, which was designed and implemented
at the MIT Lab for Computer Science several years ago. It is a DISK
sharing protocol rather than a FILE sharing protocol. It sends requests
to a server for reading and writing disk blocks by offset into the disk.
Because it is a disk sharing protocol, it sits below the filesystem,
so although you could share a disk between a UNIX and an MS-DOS system,
it wouldn't be useful because there would either be a UNIX or an MS-DOS
filesystem on that disk that one of the two systems wouldn't understand.

RVD was originally written for 4.2BSD. The VAXen at LCS all had small
disks (RK07's) and we wanted to have some disk servers to share things
like UNIX which didn't change very often, and to have some large private
disks for individual projects. RVD doesn't provide any synchronization
between disk accesses. Since synchronization would really have to
occur at a filesystem level and RVD is below the filesystem, this
is fairly reasonable. RVD allowed disks to be accessed as read only
or read write (shared or exclusive). Nobody ever wrote the companion
synchronization protocol that would be needed to allow multiple writers,
so we never used it in this mode.

Also, RVD was never a part of PC/IP. I wrote a PC/IP RVD client as a hack,
and a few people around LCS started using it. But we never got RVD packaged
up and stabilized as much as we felt was necessary in order to include
it in PC/IP, largely because of all the UNIX modications that were necessary.
There were some references to it in the PC/IP documentation, though.
I don't believe that MIT ever had an 'official' release of RVD, though a
few copies were slipped to people.

Anyway, RVD is not useful for sharing filesystems between UNIX and MS-DOS
because it's a disk protocol and not a file protocol, and
because it wouldn't allow multiple writers.

To get back to the desired goal, I would recommend one of two approaches:
	NFS - currently only available from Sun
or
	SMB over NETBIOS - put up a NETBIOS SMB server
		on the UNIX system and get NETBIOS
		for the PC and run the PC LAN program.
		NETBIOS for the PC is available from
		many vendors and there are a few
		people out there working on it for
		UNIX (try Syntax).

			- john romkey
-------