Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!watmath!clyde!cbatt!ucbvax!CLARKU.BITNET!DHASKIN From: DHASKIN@CLARKU.BITNET.UUCP Newsgroups: mod.computers.vax Subject: Load balancing on a cluster Message-ID: <8702030726.AA18052@ucbvax.Berkeley.EDU> Date: Mon, 2-Feb-87 16:23:00 EST Article-I.D.: ucbvax.8702030726.AA18052 Posted: Mon Feb 2 16:23:00 1987 Date-Received: Wed, 4-Feb-87 01:44:44 EST Sender: daemon@ucbvax.BERKELEY.EDU Organization: The ARPA Internet Lines: 52 Approved: info-vax@sri-kl.arpa Geoff Mulligan (USAFA) asks: > Does anyknow how or if a VAX clusancing between > nodes? We are not using terminal servers! Also does a cluster actually > share the memory on different nodes and if so how? What about load > balancing of jobs put in a batch queue or print queue? No, a cluster does not inherently load balance, but does allow for it to be done. First of all, terminal server load balancing is independent of the fact that you have a cluster, although I suppose the fact that a cluster can have a single network alias might allow something like that. No, a clustered machines do *not* share memory. This is an important distinction, for several reasons. Depending on your primary application(s) this may be a drawback or not. It is interesting to note that DEC decsribes the new 8974 and 8978 as 'robust' (they are rather pricy prepackaged 4- and 8-node 8700 clusters, respectively), but they can not be thought of as 'fault-tolerant' (see Digital Review for more). That is, if you're on one node and it goes down, you can then log in to another node, but you have lost your previous process. You can load-balance to some extent using generic batch queues and the cluster-wide queue manager, but it is not 'true' load-balancing... the queue manager will select the execution queue to minimize the executing job versus job limit ratio for all associated execution queues. By setting job limits creatively one could indicate to the queue manager which queues should be preferred. We run a cluster of an 8500 (20 Mb) and 2 750s (8 Mb each), with terminl servers all over the (^&&^* place, and I find that the 8500 has to get *pretty* loaded (50-60+ users) before the servers start finally putting folks on the 750s. Interactive jobs are not inherently load balanced, but you could certainly organize some procedure to do your own (that is, reject certain users on certain nodes at certain times, allow them otherwise, etc, or do a SET HOST for them -- although I've heard arguments that SET HOST is to be avoided because of the overhead). I'm sure other folks out there have done it; it really hasn;'t been a problem for us. Denis W. Haskin ------------------------------------------------------------------------ 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