	        HP's Diskless Product:  Interaction With
	      Arpa/Berkeley Services, NFS and Yellow Pages


On 7 January  1987,  Cristina  Mahon and Dave  Erickson  spoke with Dave
Gutierrez of SSO.  The talk  revolved  around the DUX project  which has
been trimmed back to provide a diskless  product.  (For lack of a proper
label, this paper will refer to the diskless product as HPD.)  Following
is a description of part of the discussion.

Unlike DUX, HPD does not have a distributed filesystem.  HPD comprises a
single  host  (call it the  pivot)  with  attached  disk and a number of
diskless  workstations  which boot, store and  retrieve  files from that
disk.  A network  among the machines  permits  this.  The network may or
may not be isolated from other HPD and non-HPD systems.

HPD will have the  ARPA/Berkeley  services (ABS) and NFS (including  the
Yellow  Pages or YP)  integrated  with it.  Both ABS and NFS/YP  rely on
daemons to coordinate  communications between processes on the local and
remote  machines.  The  particular  daemons are inetd, the ABS  internet
daemon, and the NFS/YP  daemons nfsd, biod, ypserv and ypbind.  Of these
daemons,  only  ypbind  behaves as a "client  daemon."  In other  words,
ypbind is the only daemon which exists on a  requestor's  behalf, on the
requestor's  machine.  All other daemons are "server daemons," providing
services  required  by a client.  Server  daemons  need  exist only on a
machine which makes such services available.

When ABS and NFS/YP are joined  with HPD, a  question  arises:  on which
machine(s)  of an HPD cluster will client and server  daemons run?  This
is of interest since from one external view, an HPD cluster is seen as a
single  machine  with a  single  filesystem.  From  another  view,  each
machine in an HPD cluster is an independent  processor which can respond
to requests from remote clients and originate requests on its own.

Users of each machine of a cluster are capable of making requests for YP
services.  It is  expected  that each HPD  machine  would  then have the
ypbind daemon running on it.

Since the filesystem of an HPD cluster is attached to only the pivot, it
is best that any daemons which provide file access  services be run only
on the  pivot.  nfsd, biod and ypserv are such  daemons.  These  daemons
could be run on any of the non-pivot  machines,  but 1) file access time
would be  shorter  if the  daemon  runs on the pivot and 2) the pivot is
likely to be faster and have more memory (so can support  more  daemons)
than the other HPD machines in its cluster.

Last,  ABS' inetd  would need to be run on any  machine  furnishing  the
services found in  /etc/inetd.conf.  Such services are ftp, remsh, rexec
rlogin and telnet.

Finally, if there is a cluster  formed by a server and several  discless
nodes,  an NFS  filesystem  mounted  by any of  these  machines  will be
visible to the rest of the systems in the cluster.
