At 01:50 PM 6/5/97 CDT, [log in to unmask] wrote:
>     I am considering looking into purchasing some EMC disk drives.  I
>     believe these are the ones with cache built in.  I have also
>     heard that they significantly increase system performance.  If
>     anyone can give me any feed back it would be very much
>     appreciated.  I am especially wondering about the interface to
>     the HP box.  Is it a separate card? Can one use a FW SCSI
>     interface?
>

The EMC disk subsystems are excellent machines, providing the best
performance available for all HP systems.  However, you must make an
informed decision before going for the gusto on one of these.

HP is using a ballpark figure of 100gb as the decision point for
selecting EMC as the high availability disk subsystem of choice.
(BTW, they recommend the Model 10 and 20 "Jamaica" arrays for between
50 and 100 gb and/or disk mirroring).

So, if you have greater than 100gb disk requirement, HP will recommend
that you install EMC.  I know of many sites, however, who are using
regular HP disks in a mirrored environment with plenty of success.

As far as the EMC cache, it probably won't help you very much in a
standard, OLTP environment.  In other words, it won't help very much
in an on-line Amisys environment.  MPE will do a much better job of
read elimination (the whole purpose of extensive cache anyway) than
EMC does because of Image's tight integration with the OS, and MPE's
excellent, and well-proven, prefetch algorithm.

However, the EMC cache will probably do well for you in a batch, serial-
read environment.  EMC has a self-tuning prefetch which will exceed
MPE's prefetch after a certain amount of serial I/O.

If you are looking for performance improvement from the cache, I would
recommend that, if you select EMC, you consider reducing the cache on
the EMC system and increase the amount of memory available to MPE.

That all being said, the EMC drives themselves (which are really
Seagate) are faster than any drives shipping from HP, which *will*
give you a performance boost.

EMC uses the standard HP f/w scsi cards.  Also, they supply their
own cables so you don't need to purchase separate scsi cables from
HP if you buy EMC.  EMC and HP are both very conservative in recommending
how many EMC mechanisms per SCSI card but 8 to 10 is a reasonable
number.

If you have any questions, please feel free to contact me directly.
BTW, I do not sell hardware!


Bill Lancaster