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Re: cluster

On 2002-03-29T21:07:39,
   z l <z_ling11@yahoo.com> said:

> HA module or load balancing solutions can also be
> called as cluster ? 

HA is usually achieved by "clustering" a few machines, yes. A load balancing
solution like the Linux Virtual Server etc might in fact also be called a
"cluster".

> what exactly does a cluster denote.

This is a very good question indeed; the answer isn't as straightforward as
one might hope. The word is just "slightly" fuzzy. I would, short of
recommending the excellent "In search of clusters" book by Gregory Pfister
which was already mentioned, define it as

	A cluster couples a set of nodes (servers) which have separate
	processors, memory, local storage and networking each, in such a way
	that they serve as a "meta machine" (ie, cluster) for a given job.

The "job" has different levels; from an enduser perspective, a webfarm is a
meta-machine to serve HTTP and thus might be a cluster. But to a sysadmin,
they do appear as very many separate machines to maintain, though some
techniques may be used so that they appear as a single entity for some admin
tasks etc - the job basically defines the "cluster boundary".

> implemented HA solutions like two servers, one being
> the hot standby for the other. can we call this a
> cluster ?

Yes, I would guess so.


Sincerely,
    Lars Marowsky-Brée <lmb@suse.de>

-- 
Immortality is an adequate definition of high availability for me.
	--- Gregory F. Pfister

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Linux-cluster: generic cluster infrastructure for Linux
Archive:       http://mail.nl.linux.org/linux-cluster/