sysmgr@KING.EE.UMD.EDU.UUCP (03/05/87)
Greetings and Felicitations...
In the next few weeks I will be installing a Local Area VAXcluster
which will have an 11/750 as a boot node and six VAXstation IIs as
satellites. I also have a DECserver 100 (and a DECserver 200 on the
way) which will allow terminal access to the cluster.
Here's the problem. I want to set up the DECserver so that the
user will say "Connect Cluster". It is my understanding that the
DECserver will then connect the user to the machine that is least
heavily used at the time. The problem that I forsee is that the
machine that the DECserver determines is "least heavily used" will
be a VAXstation with two users on it (all our VAXstations have
a two user maximum). I can't imagine that the DECserver would be
smart enough to avoid this, so it would dump the user to the
VAXstation, which would then, in turn, say "sorry, maximum
number of logins reached" and dump the user back to the DECserver.
Voila. The user is locked out of the cluster.
I'd be interested in hearing some suggestions as to how to avoid
this problem. Two ideas we've been knocking around are:
1) Buying multi-user licenses for all our VAXstations. The
problem with this is that our salesperson has informed
us that multi-user licenses are no longer available for
VAXstations, because too many people were buying VAX-
stations with multi-user licenses (thereby, in essence,
turning it into a MicroVAX with graphics capability) and
getting the cheaper VAXstation software licenses (cheaper
since the VAXstation is considered a "single user"
system).
2) Modifying the DECserver software so that it will do one of
two things.
a) Find the system which is least heavily used. Compare
the number of users logged in against the number
of users allowed. If they match, then repeat the
process with next least heavily used system. The
problem with this is that, although only two users
are allowed on a VAXstation, the user sitting at
the system keyboard can create multiple processes
which only count as one against the login limit.
b) Implement a "Rotary Dial" program instead of the "least
heavily used" program being used. Try to log the
user into the first VAXstation. If the login fails,
try the second, the third, and so forth. If all
VAXstations fail, dump the user onto the 11/750.
This ain't pretty, but it's an option.
I'm not a systems programmer, although I could probably hack the
DECserver software if I had the source. Has anybody else out there
done this sort of thing? Any alternate suggestions? Please respond
via any way that works.
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Christopher D. Russell, Operations Manager
Computer Aided Design Lab
University of Maryland
Arpa: RUSSELL@KING.EE.UMD.EDU Jnet: RUSSELL@UMCINCOM
RUSSELL@CINCOM.UMD.EDU UUCP: ...!seismo!umcp-cs!eneevax!russell
RUSSELL@ENEEVAX.UMD.EDU Mail: Dept. of Mechanical Engineering
Fone: (301)454-8886/454-8950 University of Maryland
College Park, MD 20742
"If growing up were fun, I'd have done it already."
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------DHASKIN@CLARKU.BITNET.UUCP (03/23/87)
Christopher D. Russell <RUSSELL@UMCINCOM.BITNET> asks: > Here's the problem. I want to set up the DECserver so that the user will > say "Connect Cluster". It is my understanding that the DECserver will then > connect the user to the machine that is least heavily used at the time. > The problem that I forsee is that the machine that the DECserver determines > is "least heavily used" will be a VAXstation with two users on it (all our > VAXstations have a two user maximum). I can't imagine that the DECserver > would be smart enough to avoid this, so it would dump the user to the > VAXstation, which would then, in turn, say "sorry, maximum number of logins > reached" and dump the user back to the DECserver. Voila. The user is > locked out of the cluster. Huh? I can't locate the correct documentation right now, and *possibly* the server software will work differently with the VAXstations, but the selection algorithm (at least with 5.1) with a LAT service is not a straight number-of-current-users, but is based on available CPU time versus number of users or something similar (I remember seeing the exact algorithm but can't locate... if someone else does, please forward to Chris). We use many servers in a cluster of 1 8500 and 2 750s, and even though the 8500 usually has 4-6 times the number of active processes as either of the 750s, the servers still prefer it much more, except in a real crunch situation. One usually has to explicitly request one of the 750s to be assigned there. Denis W. Haskin Manager, Technical Services ------------------------------------------------------------------------ DHASKIN@CLARKU.BITNET Office of Information Systems (617)793-7193 Clark University 950 Main Street Worcester MA 01610 "Anyone who _moves_ before Most Holy comes back out will spend the rest of eternity sipping lava through an iron straw." - Cerebus