changing scsi-ids of hdds

[Igor I. Shulz]

I have two hosts -
D200:
Built-in SCSI 16/5.7
HDD1 16/5.6
HDD2 16/5.5
HDD3 16/5.3
CDROM 16/5.2

and K260:
Built-in SCSI 10/12/5.7
CDROM 10/12/5.2

I'm about to connect extarnal tape-drive, which should be accessible from both of the hosts. As far as I understand I should move one of the SCSI-adapter from ID7 to ID6. I should free up ID6. Besides I shoult to move one of the CDROMs from ID2 to ID1 (for instance). And I can set ID0 on my external tape-drive. In result I'll have the next configuration:
D200:
Built-in SCSI 16/5.6
HDD1 16/5.5
HDD2 16/5.4
HDD3 16/5.3
CDROM 16/5.1
shared tape-drive 16/5.0

and K260:
Built-in SCSI 10/12/5.7
CDROM 10/12/5.2
Is it correct? If so, my question: what I should to do on my D200-host? As I see pathes of HDDs are changing on this host. What about my volume groups?

Thank

[Bill McNAMARA_1 · Accepted solution]

don't bother putting a tape on a shared bus.
A tape is a streaming devices and doesn't like interuptions.

Otherwise yes, jumper switches for the shared bus mode must ensure an initiator is at 6 and another is at 7 for example. The jumpers are adaptor specific. The devices files for the disks shouldn't change but, if you have disks on that shared bus too, the two hosts shall see them, and not necessarily by the same device file.. Make sure that you activate on one host at a time unless you've got service guard config established.

I can recall a different mechanism to share DDS' in the forums that is supported.
If you issue a search you should find the link..
I'll root around and try to get it.

Until then,
Good luck,
Bill

[LB4]

I would recommend purchasing an additional tape drive instead of sharing. If you do change the scsi ids of your disks make sure you have a good backup. Also, make sure you change the boot path to the correct disk.

[Bill McNAMARA_1]

http://forums.itrc.hp.com/cm/QuestionAnswer/1,1150,0xa184dfe5920fd5118fef0090279cd0f9,00.html

Later,
Bill

[boley janowski]

beware,

If your using a single ended type of scsi, you will have issues with distance between terminations, if you get too far usually greater than 6 feet. The errors are erronious and dont always happen, so that makes them very hard to trouble shoot.

Always had bad luck when someone has tried to share a tape drive, so i cant help you there. you would probably have better luck getting another tape drive

[Igor I. Shulz]

I take these warnings into account. But when I thought about this tape sharing I suppoused that:
- all HDDs that belong to one of the hosts BELONG to them (are used in exclusive mode) - so what about disks - I don't need serviceguard functionality.
- tape is "streaming device" and interrupt issue: as I understand anyway tape-drive is pretty generic scsi-device and uses block-writing, so host sends data-blocks and commands (in according with scsi-bus policy). It means that if I (and only I) use this device in exclusive mode from only one host in a time there should not be many problems. Or I'm wrong?

[boley janowski]

Igor,

I cant say if your wrong or not because like I said earlier I have not had good luck with the sharing tape drive thing, but if everything you said is correct, and you dont defy any of the scsi issues (distance, and duplicate id's). I wouldn't think you would have a problem, but when you do they are really difficult to trouble shoot. Good luck!

[A. Clay Stephenson]

Hi Igor,

Yes you can have a single tape drive on a single SCSI bus shared by two hosts and it works well as long as you observe the normal precautions - mainly one host at a time doing I/O.

I use this setup everyday in OmniBack. I configure the same physical drives as two logical drives - they share a common 'Lock Name' to prevent simultaneous use.

One of the logical devices is used for the actual data backup the other logical device is used to make a copy of the backup media for offsite storage. This way the backups can run at full speed during the night while the copies can run during the day without slowing down the production servers.

Clay

[Igor I. Shulz]

OK, then I'd like to come back to my first question: if I change some of pathes of ODDs on one of hosts (changing its IDs) what action should I take (along with changing boot path) to have my volume groups safe?

[A. Clay Stephenson]

Hi Igor,

I should have read your posting more carefully.
The SE SCSI on the K-box is for internal devices only; the external connector is FWD SCSI. On the D-box the external connect is SE-SCSI. It looks as though you are trying to mix single-ended and differental SCSI on the same bus - a big no-no. I suppose you could make a cable to bring the internal SE scsi cable on the K outside.
Clay

[Igor I. Shulz]

Ooops! I have to check back side of my K-host more carefully. Will check tomorrow.

Thanks

[Igor I. Shulz]

Well, you are right. It seems I cannot install shared tape on these boxes.

But my first question remains unanswered - what should I do if I change SCSI id of HDD? Especially if one of these HDDs contains /stand or /root fs ?