Thank's  Bill and everyone else who responded.  Your input is much appreciated.  I will be monitoring my disk I/O's on that volume set and I will probably add 1 or 2 drives.

Jack C.

-----Original Message-----
From:   Bill Lancaster [SMTP:[log in to unmask]]
Sent:   Tuesday, June 23, 1998 1:56 PM
To:     [log in to unmask]@inetgw
Subject:        Re: SINGLE ENDED SCSI CONTROLLER

Jack,

Oh boy, you ask some good questions.

You can still add three disks to the controller with the DDS drives.  The
only time that would create a problem is at back-up.  As far as how many
drives you can add, my standard answer applies:  "It depends".

Determining how many drives you can safely add depends on what volume per
drive you are experiencing.  Generally, you shouldn't exceed an *average*
of 20-30 I/O's per second per controller.  Though the controller can handle
upwards of 100 i/o's per second if you are averaging 20-30 you could be
bursting at a much higher level.  Therefore, if you are running 4-6 i/o's
per second per drive, I wouldn't have more than 5-6 drives per channel.
Also remember that HP's recommendation of no more than 4 drives per channel
is typically (and rightly) conservative it doesn't take into account the
nature of i/o in your particular environment.  The best thing you can do is
look at your i/o and decide if you want to take a chance with performance.
You say that the data isn't particularly critical.  If that's the case,
maybe performance isn't a huge issue either and you can then justify taking
a bit of a performance hit for the sake of greater storage capacity.

Eliminating the mirroring solves the problem while introducing another one.
 You will look high availability (not something I usually recommend) for
extendability.  Have you considered upgrading the 987 to an RX?  This gives
you a lot more expandability.

Good luck,

Bill

At 11:26 AM 6/23/98 -0400, Calandra, Jack wrote:
>        Bill,
>
>        Thanks for the info.  Unfortunately the SCSI controller for the
internal disk is also being used by 4 DDS-2 disk drives, so I think I'm out
of luck at this point.  Just how much fudging can I safely get away with?
Since I already have 4 devices per single SCSI, can I add one more?  I
currently have these devices mirrored, so I might be able to get away with
disabling the mirror and use all the drives since the data here is non
critical.  What do you think?
>
>Jack
>
>-----Original Message-----
>From:   Bill Lancaster [SMTP:[log in to unmask]]
>Sent:   Tuesday, June 23, 1998 9:16 AM
>To:     [log in to unmask]@inetgw
>Subject:        Re: SINGLE ENDED SCSI CONTROLLER
>
>Hi Jack,
>
>HP recommends no more than 4 drives per single ended SCSI controller.  Even
>if you fudged that a little, 10 is *way* too many.  You would likely end up
>with serious disk I/O performance problems.  Are you sure about the slot
>space??  Isn't there another s/e SCSI controller used for the internal disk
>and the DAT drive?
>
>
>Bill
>
>At 09:48 AM 6/23/98 -0400, Calandra, Jack wrote:
>>I have 4 HP6000 mass storage systems installed in my 987sx.  Each system
>has 2 3.5' half height 2 gig. Drives installed. The mass storage systems
>are paired off onto two separate single ended SCSI controllers.  Each
>controller has 4 devices presently connected to it.  I would like to max.
>out each system by adding 3 more 2 gig drives to each 6000 system.  That
>would make a total of 10 devices per single ended controller.  My problem
>is that I do not have any additional slots available to add more
>controllers and fast wides are not an option.  So my question is, how many
>devices are supported on a Single Ended SCSI controller and how do I set
>the SCSI address switches??
>>
>>Any help would be appreciated
>>
>>Jack Calandra
>>AIG New York
>>
>>
>
>