James Lagger wrote:

> We are about to install a new (used) Model 20 nike disc array for
> the system volume set. The array is missing a battery part# A3254A.
>
> The sales rep claims this battery is optional and not necessary. If
> added it would provide disc caching but would be of little benefit
> in our situation with only two system discs mirrored.

The battery is required to insure write integrity on the overall
array.  The Nike series array controllers have cache used in both
reads and writes (write completion is signalled to the system once
the data is in the cache even if not yet written to disk).  The
battery doesn't "enable" cache, it protects it.  And your UPS issue
is only one source of potential pain, it can be hosed in other ways.
If you are looking for a relatively bullet-proof solution and you
have redundant power supplies, fans, controllers, etc., you would be
compromising yourself without that battery to backup the cache.  But
since the 3000 implementation doesn't support alternate paths yet,
it may be somewhat of a moot point.

Automatic switchover to an alternate path was mentioned to be in the
works at IPROF 99, but I haven't seen any evidennce of it yet.

Jeff Kell <[log in to unmask]>