changing SSA cableing

[chelldis]

Our SSA d40 cabinet has been having link issues for a long time. IBM and other companies have looked at it, but no one seems to know what the issue is. I have been looking at it and figured I would first try to get the machine in proper condition (it has been poorly maintained by another company for years, and turned over to us without any documentation or anything)
First of all I want to re-cable the SSA cabinet, It is now connected on one adapter as followed a1-1, a2-4, b1-9, b2-12. The cabinet has 5 physical disks which are not part of a RAID. Just for proper order and to have a working loop I want to re-cable it from ports 1 to 8 and from 9 to 16.

My question is, does re-cabling mess with virtual or physical disk names or positions? Are there issues I should consider?

 

[p5wizard]

I would not change the cabling setup. Looks fine as it is

If you have 3 disks or less in 1 loop, it is better to use 1 quadrant of an SSA drawer, as it is better to have an active SSA node (i.e. disk) next to a cabled port.

You state that in total you have 5 disks on 2 loops, so it should be something like

a1-cable-d40/1-disk=1-disk=2-blank=3-disk=4-d40/4-cable-a2
b1-cable-d40/9-disk=9-blank=10-blank=11-disk=12-d40/12-cable-b2

in both your a1-a2 and b1-b2 loops there should be a disk module in the positions where your cables connect to.

The other -unused- positions (5-8 and 13-16) should contain blank or dummy modules.

if you want to extend the loops to 8 positions each, you need at least 4 disk modules per loop i.e.:

a1-cable-d40/1-disk=1-blank=2-blank=3-disk=4-disk=5-blank=6-blank=7-disk=8-d40/8-cable-a2

I this example, a disk module is needed next to the ports 4 and 5 in order for the automatic link between port 4 and 5 of the SSA drawer to function properly. That's what I've always been told...

Do
lsdev -Ccpdisk
or
lsdev -C|grep -i ssa
to show the positions in the drawer for your 5 pdisks and see if your loops check out with my guesses. If not, post the output here and I will have a look...



HTH,

p5wizard

 

[RMGBELGIUM]

some good tips for SSA loops :

1.try to have a disk on the first and last position between all bypass cards.If loops go open , most of the times, there's a dummy on the start or end of a quad.
2.update your diskfirmware to the latest level, and firmware of ssa adapters.


I'd go with p5's proposal for building your disk loops
Perhaps also consider replacing the ssa cables between cards and drawer, then you can rule out faulty cabling as well.If you still have open loops, if the open loop keeps occuring in the same place, consider having bypass cards replaced.We've had open loops on different occasions, and the causes were :

defective bypass cards
defective disks ( the disk didn't give any errors )
dective backplain for the D40
microcode level disks to low
defective cabling
a dummy instead of a disk at the beginning of an ssa loop

regards,

R.

 

[DukeSSD]

With only 5 disks you should not cable the whole drawer in.
You should have a disk in each slot next to a bypass card and must not have more than 3 dummies in a row, so the minimum number of disks for a whole drawer is 8.
i.e. 'a' loop fron 1 to 8 would need a disk in 1, 4, 5, 8 and the 'b' loop would need a disk in 9, 12, 13 and 16.
Stick with the 1 - 4 and 12 - 16 and make sure you have a disk in 1, 4, 12 and 16.
If you have a #6225, #6230, 4-p card make sure the cables are blue, not black. They have extra wires and allow the full speed of the T40 / D40 drawers.