Buying a Lispm Server [?]

[Chris Lindblad <CJL@REAGAN.AI.MIT.EDU>]

    Date: Tue, 20 Jan 87 19:32:59 -0100
    From: unido!gmdzi!jc@seismo.CSS.GOV (Juergen Christoffel)

    My company is just about to buy a server machine for our 18 symbolics machines
    and I'm engaged into the decision making process. And now I'm wondering...

    Buy a lispm?
	    Seems to be the best server for serving lispms only?

Here at the MIT AI lab we have have for one of our main file servers for our
70 lisp machines a 3650 configured with 16 MB of memory, a CDC 368 MB disk
drive, and 4 Eagle disk drives. This server does all the namespace (which
turns out to be a pretty big load here) and sys host serving for all our
machines. We are also running it as our mail server, and it handles a load of
about 30 simultaneous users with no problem at all.  It looks like we could
increase the load on the machine by 50% before it would be a problem.

    What model? 3675?
	    ... should be a really fast server

A 3645 with the SMD disk controller and CDC 368 MB disk drive is just as fast
as a 3675, and a lot cheaper (especially if you can get a deal on it). Anyway,
in my opinion you don't need an IFU/XSQ machine for a server. The better thing
to get on a server is extra memory.

    What memory needs a server-only machine? 4MB? 8MB? Or even more?
	    Will 4MB be sufficient? All our symbolics here have at least 8MB...
	    and it will run the mailer, a print spooler, and some goodies :-)

8MB will work fine, unless your machine is gonna be real busy. We have 16MB on
our servers, but we also have 70 lisp machines and very big namespaces.

    What disk[s]?
	    515MB? An eagle? One? Or two in order to keep paging and lmfs apart?
	    It should store all sources, the namespace, documentation and even some
	    of our projects' files.

The way we have our machine set up is that all the microcode, world load
files, boot files, flod files, and paging files are on the CDC 368MB disk
drive we use as fep0, and we keep our lmfs files on the four eagles connected
to the machine via the disk multiplexor board that symbolics sells. I would
suggest for you to start off with either a 3640 or a 3650 with a 368MB disk
drive and 8MB of memory, and then to get an Eagle or a 515 MB disk drive, and
to create a lmfs file partition on it. When you create the lmfs partition on
the disk, leave a hundred or so blocks free in the fep filesystem, just in
case some bad blocks develop on the lmfs file partition, and they have to be
patched out and replaced. If you wanted to expand, you would then buy a
multiplexor from Symbolics whan you get the third disk. With the multiplexor,
you can put up to 8 disks on your machine.


    What's about backup?
	    Is a streamer sufficient? Does a *real* tape drive provide faster
	    backup? [Or is it slower?]

Our experience has shown that the cartridge tape drive is hardly sufficient
for doing regular backups of lisp machines file systems. You're probably
better off getting the real tape drive and doing regular dumps to it instead.
The only trouble I have with recommending this approach is that the tape drive
that Symbolics sells does not have the capability to read and write 6250 BPI
tapes. It only goes up to 3200BPI. I have heard that the Cypher Series M990
GCR Cachetape uses the same interface as the Cypher tape drive that Symbolics
sells, but also has 6250BPI capability, and works fine on the lisp machine.
You could use this tape drive provided you buy the controller board that goes
into the lisp machine from Symbolics.

What we actually do here at the AI lab is use the chaos RTAPE protocol to
backup our lisp machine filesystems to 6250BPI tape drives we have on our
vaxes running UNIX. 

    Your experience is welcome!
    Anybody made some pereformance measures? Some tricks in configuring such a 
    server machine? ... besides increasing wired lmfs-buffers and the like...

We have built a file-server init file based on the file in the sys:examples;
directory, but also with a lot of other stuff. I'll mail it to you if you want
to see it.

    P.S. One minor problem: should one still buy a 3640 today?

If you have a lot of 3640's this might be a good idea. Suppose that some part
in your server machine breaks, and it might be a while until you can get it
fixed. Instead of just sitting there with all your files unavailable, you can
swap parts with some other machine that you have, and get your server working,
and just leave the other machine broken for the interim. If you have 3620's
and 3650's, then it's probably a better idea to get a 3650 file server for the
same reason.

Right now (Release 7.0G1) 3650's are probably just a little bit slower than
3640's as file servers. The processor is a faster, but the disk io is a
slower. It is my understanding that disk io on 3650's is substantially
improved in Release 7.1, though, and a 3650 will probably be faster than a
3640. Serial io is supposed to be better on 3640's than 3650's, so if you're
going to be print spooling, all other things being equal, you might want a
3640.

All in all the two machines are still close to equal in terms of server
activity (provided you use SMD disks). It is my impression that main reason
that Symbolics has come out with the 3650 is that it's cheaper to make. As
long as that is not reflected in the price of the machines it shouldn't be a
factor in what machine you want to buy.