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
>>
>>
>
>