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K-class SCSI ID and HW path question

 
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Philip Kime
Regular Advisor

K-class SCSI ID and HW path question

We have a rented old K-class 580 that was delivered with the four disks in the front (non hot-swap) in the wrong places according to the HW assignment map on the door. This became apparent in an amusing way when replacing a failed disk last week (don't ask ... one normally should get clues from disk LEDs, failed disks coming back online etc. but the set of coicidences that conspired to make these clues misleading were amazing ...)

Anyway, it looks like this:

Bay C: HW path 10/0.3.0 (c0t3d0)
Bay D: HW path 10/0.4.0 (c0t4t0)
Bay E: HW path 10/0.5.0 (c0t5d0)
Bay F: HW path 10/0.6.0 (c0t6d0)

and it should be, according to the front panel map:

Bay C: HW path 10/0.6.0 (c0t6d0)
Bay D: HW path 10/0.5.0 (c0t5t0)
Bay E: HW path 10/0.4.0 (c0t4d0)
Bay F: HW path 10/0.3.0 (c0t3d0)

We have many peopl who might replace a disk on this machine so I want the front panel paths to be correct. Am I right in assuming that it's only the SCSI jumpers on the disk that determine these paths (and device numbers) so I can just move the disks around to the right places according to the ID and it will be ok? Obviously, I can't change the jumpers because that would change the device numbers and that would break LVM completely (there are root disks and mirrors).

7 REPLIES 7
curt larson_1
Honored Contributor
Solution

Re: K-class SCSI ID and HW path question

Am I right in assuming that it's only the SCSI jumpers on the disk that determine these paths (and device numbers) so I can just move the disks around to the right places according to the ID and it will be ok?

yes, you are correct

Obviously, I can't change the jumpers because that would change the device numbers

correct again, this would be very bad
Hoefnix
Honored Contributor

Re: K-class SCSI ID and HW path question

Ok, if it's not Hot-swap, it will be junpered disks (I have sort of the same situation at home with a D210 system, disk are jumpered)). So I think you are right. The disks are all on the same bus, so when moving the disks to another bay in the K-class server would do you trick.

Do not re-jumper the disks, because then ,like you already noticed, LVM-config will be corrupted.

Regards,

Peter Geluk
Philip Kime
Regular Advisor

Re: K-class SCSI ID and HW path question

Ok, thanks chaps, I thought as much. A manager here said "you can just move the jumpers around on the disk can't you?" I didn't like to emphasise just how bad that would be for the root disks :-)
Ray Carlson
Frequent Advisor

Re: K-class SCSI ID and HW path question

Why don't you take the easy route and just change the labels on the front panel? Or put stickers over them with the correct information. No downtime and no hardware changes!
Jeff Schussele
Honored Contributor

Re: K-class SCSI ID and HW path question

Although labels are nice, I never trust them.
I always do a dd read on the drive - if responding - and look for the constant drive activity light. If not, it'll be the one that doesn't light up.

Rgds,
Jeff
PERSEVERANCE -- Remember, whatever does not kill you only makes you stronger!
Ken Burke
Advisor

Re: K-class SCSI ID and HW path question

Hi Philip,

You are correct it is only the jumpers on the discs that are used for the K class internal discs.

You could just move the discs around, but the SCSI cable can be quite tight and you might cause more problems than you solve.

Ken
Robert Kerr
Advisor

Re: K-class SCSI ID and HW path question

You can dd from each device out to null and check the steady lights to know where your disks are really at.

something like:

dd if=/dev/dsk/c10t2d0 of=/dev/null

and break it (may take a moment to actually stop) when you've identified the disk you're reading.