Martha Friedrich wrote:

> With the ongoing changes in disc technologies and HP's moves to keep
> up, I find it hard to distinguish the best critieria for selecting
> additional drives for my 957. I found several articles in the archives
> and couldn't tell which element has more importance.

[...big snip...]

> ------------------QUESTIONS BEGIN-----------------
> Do I stay away from the drives with "write-on-arrival" to avoid buying
> a UPS?

Almost all HP-label drives remaining require a UPS and do not support
sector atomicity; I haven't heard any firm statements of which models
do/don't support this feature, but as far as I know, the 302x and 304x
SE SCSI drives were the last to include this "for sure".  Corrections
to this statement most welcome.  Still, a UPS for these drives is not
a major expense and is highly recommended.  Your older HP-IB drives
should be OK (and draw more current, so bad on an inexpensive UPS).

> Do I want to have many drives (spindles) and avoid reducing my config
> down to a few high capacity drives (8GB) for performamce advantages?

In general, reducing spindle count decreases your I/O bandwidth.  There
are ways to counter the problem, but as a general rule, more spindles
are better for performance while you tradeoff a higher probability of
unit failure.

> Do I avoid a mixed drive size environment and try to use drives of the
> same size & speed?

Don't use a high-capacity drive as ldev 1 as MPE will reserve 50% of the
drive at all costs.  Some may argue the merits of using a RAID array as
ldev 1 (since you can't mirror the system volume set) but this appears
to the system as one logical unit, and all paging/transient I/O will be
to this single device if you have volume sets defined.  You need some
figures for paging rates, etc., to know for sure if this is an option.

> When do I need to consider an additional SCSI channel to keep optimal
> I/O performace?

This is a very relative value and dependent on your environment.  You
did not mention user volume sets, so it would be largely dependent on
file placement.  If you had a volume set, isolating the system volumes
on one channel(s) apart from the application volume set channel(s) does
guarantee a boost by separating paging I/O from application I/O.  As
for your tape drive, it depends on how quickly you want your backup to
run.  Ideally the tape has it's own channel, but few of us can afford
such a luxury.

> I have three 2GB, three Blitz's (670mb), one 4GB & one 1.3GB drive.
> The Eagles & Blitz's are on HPIB, the 4GB shares a SCSI with a tape
> drive and the three 2GB along with the 1.3 share a SCSI with another
> tape drive.  I have only one volume set, the SVS.  I have one
> application that uses 10 databases and some 200 non-concurrent users
> (average 80 con-current).

> I would like to replace the two Eagle drives because of their high
> maintenance costs with a 4GB drive to maximize the usage of cabinet
> slots and eventually replace the Blitz's as well.  I have plenty of
> disc space so the replacement with a "High" capacity drive is not the
> driving force.

I don't know a "Blitz" unless it's a Coyote (?) but at any rate, get
rid of the HP-IB stuff for SCSI.  Without knowing any other details,
I'd say get a couple of 4Gb drives.  Use some (3) 2Gb drives to make
a system volume set, and the balance as user volume set for your
applications.

Jeff Kell <[log in to unmask]>