SE-SCSI bus question on D370

[Maarten van Maanen]

I have a question concerning the SE-SCSI bus on a HP900 D370. We have one with HP-UX 11.0 which is to be used for an important Oracle test. However, there was only one 4.3Gb and one 9Gb disk in it. Delivery time for extra FWD disks is about four weeks and this is far too long. So, I hooked up another Hp but non-UX external box to the SE-SCSI connector on the back of the D370 and installed five IBM 9Gb disk in it for a total of 45Gb. First I had some trouble getting all disks recognized due to SCSI-ID's but now I get to see them all with ioscan (output below).

disk 7 8/16/5.1.0 sdisk CLAIMED DEVICE IBM DNES-300
/dev/dsk/c1t1d0 /dev/rdsk/c1t1d0
target 5 8/16/5.2 tgt CLAIMED DEVICE
disk 2 8/16/5.2.0 sdisk CLAIMED DEVICE TOSHIBA CD-ROM A
/dev/dsk/c1t2d0 /dev/rdsk/c1t2d0
target 6 8/16/5.3 tgt CLAIMED DEVICE
disk 4 8/16/5.3.0 sdisk CLAIMED DEVICE IBM DNES-300
/dev/dsk/c1t3d0 /dev/rdsk/c1t3d0
target 7 8/16/5.4 tgt CLAIMED DEVICE
disk 6 8/16/5.4.0 sdisk CLAIMED DEVICE IBM DNES-300
/dev/dsk/c1t4d0 /dev/rdsk/c1t4d0
target 8 8/16/5.5 tgt CLAIMED DEVICE
disk 5 8/16/5.5.0 sdisk CLAIMED DEVICE IBM DNES-300
/dev/dsk/c1t5d0 /dev/rdsk/c1t5d0
target 9 8/16/5.6 tgt CLAIMED DEVICE
disk 3 8/16/5.6.0 sdisk CLAIMED DEVICE IBM DNES-300
/dev/dsk/c1t6d0 /dev/rdsk/c1t6d0

The question now is the following:
On the SE-SCSI bus I see five disks, 1 Toshiba CD-Rom player and 1 DAT-drive for a total of 7 devices. However, on SE-SCSI, there can only be 7 devices INCLUDING the SCSI-controller. So how is it I can attach (and see) seven devices apart from the controller.
Next question this if I will get into trouble using this configuration.

[melvyn burnard]

No, on SE SCSI you can have eight devices including Interfaces.
So address 7 (highest priority) is the Interface or controller, then 6, 5, 4, 3, 2, 1, 0 are the devices.
You now have a fully loaded bus, and this means ALL i/o goes down a single bus. Expect it to be SLOW.
You also need to look at the maximum cable length of 6 metres MAXIMUM.

[Alexander M. Ermes]

Hi there.
Do yourself a favour to enhance performance.
Get another SE-SCSI interface and hook the CDROM and the DAT drive to it. That will take off load in case of a backup, tar, cpio or else to tape. If you want more improvement,
get one more inetrface to split the disks between two interfaces. That would mean three interfaces, but it would really improve your performance, especially for databases.
Rgds
Alexander M. Ermes

[paul courry]

Get another SE-SCSI interface and hook the
CDROM and the DAT drive to i

Um, I don't have either a box or a manual in front of me, but it looks like the CD-ROM and DAT drive are *internal* to the box. This means that while he needs another SCSI card, it would be the IBM drives that would get hooked to it.

FYI, for performance reasons the maximum recommended number of items on a single-ended SCSI card should be 5 (10 for fast-wide). Another FYI, as long as the CD-ROM and DAT drive are quiet and *not used* (there is little traffic on the bus from quiet devices) there should be no performance problem. HOWEVER, the minute you use them, Wham!, you will start having performance problems and possibly bus contention problems. If you can afford it, get another card.