topic Re: Disk Storage SC10 in Disk Enclosures

Disk Storage SC10

Radim Jarosek — Mon, 27 May 2002 10:13:42 GMT

Hi all,

I need some advice, because I'm confused with SC10.
I don't know if I clearly understand this. For explanation. We have L1000 server with SC10 - 4 old disks (18GB) and last week we bought 4 new disks (36 GB). Here is output from ioscan :

Class I H/W Path Driver S/W State H/W Type Description
======================================================================
disk 0 0/0/1/1.2.0 sdisk CLAIMED DEVICE SEAGATE ST39204LC
/dev/dsk/c1t2d0 /dev/rdsk/c1t2d0
disk 1 0/0/2/0.2.0 sdisk CLAIMED DEVICE SEAGATE ST39204LC
/dev/dsk/c2t2d0 /dev/rdsk/c2t2d0
disk 2 0/0/2/1.2.0 sdisk CLAIMED DEVICE HP DVD-ROM 304
/dev/dsk/c3t2d0 /dev/rdsk/c3t2d0
disk 3 0/3/0/0.0.0 sdisk CLAIMED DEVICE SEAGATE ST318404LC
/dev/dsk/c4t0d0 /dev/rdsk/c4t0d0
disk 4 0/3/0/0.1.0 sdisk CLAIMED DEVICE SEAGATE ST318404LC
/dev/dsk/c4t1d0 /dev/rdsk/c4t1d0
disk 11 0/3/0/0.2.0 sdisk CLAIMED DEVICE HP 36.4GST336752LC
/dev/dsk/c4t2d0 /dev/rdsk/c4t2d0
disk 12 0/3/0/0.3.0 sdisk CLAIMED DEVICE HP 36.4GST336752LC
/dev/dsk/c4t3d0 /dev/rdsk/c4t3d0
disk 5 0/3/0/0.8.0 sdisk CLAIMED DEVICE SEAGATE ST318404LC
/dev/dsk/c4t8d0 /dev/rdsk/c4t8d0
disk 6 0/3/0/0.9.0 sdisk CLAIMED DEVICE SEAGATE ST318404LC
/dev/dsk/c4t9d0 /dev/rdsk/c4t9d0
disk 13 0/3/0/0.10.0 sdisk CLAIMED DEVICE HP 36.4GST336752LC
/dev/dsk/c4t10d0 /dev/rdsk/c4t10d0
disk 14 0/3/0/0.11.0 sdisk CLAIMED DEVICE HP 36.4GST336752LC
/dev/dsk/c4t11d0 /dev/rdsk/c4t11d0
disk 7 0/7/0/0.0.0 sdisk CLAIMED DEVICE SEAGATE ST318404LC
/dev/dsk/c5t0d0 /dev/rdsk/c5t0d0
disk 8 0/7/0/0.1.0 sdisk CLAIMED DEVICE SEAGATE ST318404LC
/dev/dsk/c5t1d0 /dev/rdsk/c5t1d0
disk 15 0/7/0/0.2.0 sdisk CLAIMED DEVICE HP 36.4GST336752LC
/dev/dsk/c5t2d0 /dev/rdsk/c5t2d0
disk 16 0/7/0/0.3.0 sdisk CLAIMED DEVICE HP 36.4GST336752LC
/dev/dsk/c5t3d0 /dev/rdsk/c5t3d0
disk 9 0/7/0/0.8.0 sdisk CLAIMED DEVICE SEAGATE ST318404LC
/dev/dsk/c5t8d0 /dev/rdsk/c5t8d0
disk 10 0/7/0/0.9.0 sdisk CLAIMED DEVICE SEAGATE ST318404LC
/dev/dsk/c5t9d0 /dev/rdsk/c5t9d0
disk 17 0/7/0/0.10.0 sdisk CLAIMED DEVICE HP 36.4GST336752LC
/dev/dsk/c5t10d0 /dev/rdsk/c5t10d0
disk 18 0/7/0/0.11.0 sdisk CLAIMED DEVICE HP 36.4GST336752LC
/dev/dsk/c5t11d0 /dev/rdsk/c5t11d0

I suppose, we have two controllers, the first is 0/3 and the second is 0/7.
When I'd set mirroring with two controllers, I should use for 0/3/0/0.1.0 and 0/7/0/0.1.0. Am I right ?

Thanks in advance for your help

Radim

Re: Disk Storage SC10

Duncan Edmonstone — Mon, 27 May 2002 11:09:41 GMT

You can't *mirror* between 0/3/0/0.1.0 and 0/7/0/0.1.0 as they are in fact the same disk... you *can* set up an alternate link to this disk though:

(I'm assuming your using LVM)

pvcreate /dev/dsk/c4t1d0
mkdir /dev/vgNN
mknod /dev/vgNN/group c 64 0xNN0000
vgcreate vgNN /dev/dsk/c4t1d0
vgextend vgNN /dev/dsk/c5t1d0

Now if you do a vgdisplay -v vgNN you should see /dev/dsk/c5t1d0 as an alternate link to c4t1d0

HTH

Duncan

Re: Disk Storage SC10

Vincent Farrugia — Mon, 27 May 2002 11:31:24 GMT

Hello,

In order to mirror, you must have an additional SC10, and then mirror across SC10s.

Else, you can configure the SC10 into split bus mode, only then you can mirror across controllers.

Split bus mode splits the SC10 into 2, 5 disks read by controller A and 5 disks read by controller B. You can mirror across controllers this way. In order to put the SC10 into split bus mode, put the first switch on both controllers into the 0 position.

However, be aware that the hardware paths will change, i.e., ioscan will yield different hardware paths and device paths.

HTH,
Vince

Re: Disk Storage SC10

Vincent Farrugia — Mon, 27 May 2002 11:38:51 GMT

And, of course, power off SC10 and L server before pulling down the switch... :-)

Re: Disk Storage SC10

Radim Jarosek — Mon, 27 May 2002 11:47:30 GMT

Hi,

I see, that's right. However, why would I need alternative link ?

Can you tell me why I have two HW path ?
I assume that I have 2 controllers. And I can mirror between them.

0/3/0/0.0.0 1 LVM vg01 17366 SEAGATE ST318404LC
0/3/0/0.1.0 1 LVM vg01 17366 SEAGATE ST318404LC
0/3/0/0.10.0 1 Unused -- 34732 HP 36.4GST336752LC
0/3/0/0.11.0 1 Unused -- 34732 HP 36.4GST336752LC
0/3/0/0.2.0 1 Unused -- 34732 HP 36.4GST336752LC
0/3/0/0.3.0 1 Unused -- 34732 HP 36.4GST336752LC
0/3/0/0.8.0 1 LVM vg01 17366 SEAGATE ST318404LC
0/3/0/0.9.0 1 LVM vg01 17366 SEAGATE ST318404LC
0/7/0/0.0.0 1 Unused -- 17366 SEAGATE ST318404LC
0/7/0/0.1.0 1 Unused -- 17366 SEAGATE ST318404LC
0/7/0/0.10.0 1 Unused -- 34732 HP 36.4GST336752LC
0/7/0/0.11.0 1 Unused -- 34732 HP 36.4GST336752LC
0/7/0/0.2.0 1 Unused -- 34732 HP 36.4GST336752LC
0/7/0/0.3.0 1 Unused -- 34732 HP 36.4GST336752LC
0/7/0/0.8.0 1 Unused -- 17366 SEAGATE ST318404LC
0/7/0/0.9.0 1 Unused -- 17366 SEAGATE ST318404LC

For example :
0/3/0/0.0.0 and mirroring with 0/7/0/0.1.0

Vince:

I'd try it, but on 4 disk I have data. Could I lost it ?

>And, of course, power off SC10 and L server before pulling down the switch... :-)
Good point ;)

Radim

Re: Disk Storage SC10

Duncan Edmonstone — Mon, 27 May 2002 11:56:06 GMT

Why would you need an alternate link? Well these are usually used in conjunction with disk mirroring to increase availability... If one 'link' to a disk fails (because of the SCSI card or cable) then the other can be used. Not much use if all your data is on a single disk and this fails though. Also with the correct hardware and software (not LVM and SC10 I'm afraid) alternate paths can be used to load-balance I/O and enhance performance.

HTH

Duncan

Re: Disk Storage SC10

Bill McNAMARA_1 — Mon, 27 May 2002 12:03:01 GMT

A quick way to test which disk is which..

dd if=/dev/dsk/c4t10d0 of=/ddev/null

The led of the disk will light up during the read.

It is possible to configure the SC10 in split bus mode, in which case the path would not be an alternative path.. and therefor you couldn't do alternate paths as illustrated above. You would have hald the device files in that case too.

In your config, the disk will still be a SPOF, single point of failure, but the controller or cable won't be.

If you want to eliminate SPOFs you need to split the bus internally in the SC10 via a dipswitch, and then mirror.

Read the SC10 admin manual.
for more on that,

Later,
Bill

Re: Disk Storage SC10

Vincent Farrugia — Mon, 27 May 2002 12:03:45 GMT

Hello again,

First point:

You can't mirror between controllers at the moment because you are in full bus mode. That is, both controllers control all the disks (10), so as to provide redundant paths. That's why at the moment you can only make an alternate path and not mirroring.

In split bus mode, however, you have 5 disks controlled by 1 controller and the other 5 by the other. Controller A controls disk 1, 3, 5, 7 and 9 and controller 2 controls the rest. So in this scenario, you can mirror like this: disk 1 with 2, 3 with 4, 5 with 6 etc.

Second point:

Your LVM will be havoced when you do split bus mode since the hardware paths are changed. You need to backup all your data, redo the VGs and LVs of your SC10, and restore.

HTH,
Vince