Advice wanted on fileservers and net-loading.

[Paul Leyland]

I would welcome advice, thoughts and opinions on the following problem.
How do we upgrade a small-to-medium size system into a medium-to-large
size one?

At present, we have a network of 10 diskless Sun-3's (mostly 3/50's) and 5
diskful machines: a 4/260C, three 3/160C's and a 3/180S file server.  The
3/180 provides root, pub and swap space for all the diskless machines; the
diskful machines provide local swap and SunOS, but mount users filesystems
and local system software from the server.  The 3/160's have 140Mb SCSI
disks; the 4/260 has a 560Mb SMD disk; the 3/180 has two Eagles on a 451
controller and a 1.4Gb NEC disk on an Interphase 4400 controller.  The
server is also used for tape backups, printing, mail, gatewaying to the
campus ethernet and so on.  Direct logins on it are strongly discouraged
so to give more performance for the rest of the net.

In the next few months, we will be getting several diskless 4/100's and a
couple of diskful Sun-4's.  All of this lot will add to the load on the
ethernet (currently running at about 25% loading within factor two) and on
the server (typically, 50% system cpu, 45% idle, 5% user) and it is clear
that we need more power in the system.

The question is: how can we best achieve this?  "Best" includes ease of
adminstration, floor-space required and maintenance, as well as low cost.

Two solutions come to mind.

First, we could get a 4/260 with one or more big disks; split the ethernet
with a bridge (I believe they act as smart filters and pass only those
packets which need to reach the other half, absorbing the others.
Confirmation?) and put half the net on that new machine.  I want to avoid
using a whole new sub-net if possible.  Users' filesystems would also be
split across the two machines.

Secondly, we could get several small (300Mb ?) disks and plug them into
currently diskless machines.  Each of those would be a server for one or
two of the remaining diskless machines.  Users' filespace would be
increased by that saved from the client partitions now in use.  In
addition, we may be able to add another disk to the current server to
increase users' space.

At present, I favour the first but I can see that it may be rather more
expensive.  The arguments against the second, as I see it, are that
backing-up many more machines is a hassle and uses more tapes and time
(both of which mean money also); the ethernet loading is not reduced
*that* much; and machine-loading.  Does any one know whether a 4/110 or
3/160 can happily serve 1 or 2 others *and* run suntools and a "typical"
application mix, all without server and clients suffering badly?  Does it
help if only the same architectures are served?  (Clearly, it requires
less disk space, but does it take fewer computrons as well?)

Thanks if you can help out.  If I get direct mail, I'll summarize
afterwards.

		Paul Leyland

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