.\"
.\" 5799-WZQ (C) COPYRIGHT IBM CORPORATION 1986,1987,1988
.\" LICENSED MATERIALS - PROPERTY OF IBM
.\" REFER TO COPYRIGHT INSTRUCTIONS FORM NUMBER G120-2083
.\"
.\"$Header:rvd.4p_ca 11.0$
.\"$ACIS:rvd.4p_ca 11.0$
.\"$Source: /ibm/acis/usr/man/man4/RCS/rvd.4p_ca,v $
.\"This file contains -man macros.
.TH RVD 4P "July 1987" "Space overwritten by .AC macro" " "
.AC 1 0
.SH NAME
rvd \- Remote Virtual Disk protocol
.SH DESCRIPTION
RVD
is a network service which allows several
physical machines to share one
physical mass storage device such as a hard disk.  The basic
concept is to have the machine to which the device is physically attached
act as a server to read and write blocks for all the other
machines desiring use of the resource.
.PP
The server program apportions the
physical blocks into \*(lqvirtual disk packs\*(rq based on a
table maintained with
.IR vddb (8).
The packs can then be used separately by clients.  There are
three modes of use: read-only, shared, and exclusive.
Exclusive mode is used for
read-write access, while read-only mode is as it sounds.
Shared mode is not supported under IBM/4.3.
If a disk pack is \*(lqspun up\*(rq in read-only mode,
several clients may share the pack and read its information.  In
exclusive mode, one client has exclusive use of the disk pack.
.PP
Packs are \*(lqspun up\*(rq and \*(lqspun down\*(rq with the 
.I up
and
.I down
commands (see
.IR up (1)).
This can be done 
at reboot time within
.I /etc/rc.local
(see
.IR rc (8))
or
at login time within
.I ~/.login
(see
.IR csh (1)).
Once a pack is spun up, it behaves like a disk physically attached to
the local machine (excepting network latency).
The client can do anything desired with the pack;
both MS-DOS and UNIX operating system file systems have 
been used on the same physical
drive at the same time (on separate packs, of course).
.PP
RVD
is implemented in two parts: server code and client code.  The server
code is written as a
.IR "user process" ,
i.e. it does not require any special
privileges beyond read/write access to the disks it manages.  The server
opens a network socket and listens for UDP connections.  It also accepts
all
RVD
packets and acts on them.
RVD is a protocol different from both
UDP and TCP,
although similar in nature to the former.
.PP
The client code is implemented as a pseudo-device and corresponding
device driver in the kernel.  It can handle up to 10
remote virtual disks
simultaneously, which are associated with the pseudo-devices below.
.SH FILES
.DT
/dev/vd[0-9]a		block special file pseudo-device
.br
/dev/rvd[0-9]a		character special file pseudo-device
.SH "SEE ALSO"
up(1), rvddb(5), rvdtab(5),
rvdflush(8), rvdchlog(8), rvddown(8),
rvdexch(8), rvdflush(8), rvdlog(8), rvdsend(8), rvdshow(8),
rvdshut(8), rvdsrv(8), savervd(8), 
spinup(8), vddb(8), vdstats(8)
.br
``The Remote Virtual Disk System'' in Volume II, Supplementary Documents