RAID 0+1 with LVM on HP-UX 11i

[Robert Milne]

Hello all,

I am looking for advice on how it is possible to setup mirroring & striping using LVM on a 9000 L1000 with Ultra3 SCSI disks. There are 8x HP 18.2Gb disks on two SureStore shelves. Four disks (one shelf) are connected to SCSI instance 5, path 0/4... and the other four in the other shelf to instance 8, path 0/7...

When the requirement was put to our HP install engineeer, the four disks c5t0d0 c5t2d0 c8t0d0 c8t2d0 were configured in PV0 and c5t4d0 c5t6d0 c8t4d0 c8t6d0 in PV1. A single, mirrored logical vol was then created for 65GB using PVG strict policy.
Here is the lvdisplay currently:
--- Logical volumes ---
LV Name /dev/vg03/lvol1
VG Name /dev/vg03
LV Permission read/write
LV Status available/syncd
Mirror copies 1
Consistency Recovery MWC
Schedule parallel
LV Size (Mbytes) 65000
Current LE 16250
Allocated PE 32500
Stripes 0
Stripe Size (Kbytes) 0
Bad block on
Allocation PVG-strict/distributed
IO Timeout (Seconds) default

Now while I am confident this is mirrored, I am not so sure about the stripe status. I don't think it really is, true ?

I have also since realised that while the interleaving of the disks over the two SCSI busses is good, we have a single point of failure in that each of the shelves only has one power supply. If a supply goes I lose the lot ! This lvol is to be used for our database (much more read than write) so redundancy and read performance is important. I also have little money to spend on RAID controllers etc.

I was thinking now I should change the config. to put four disks on a stripe set, on one shelf/channel, mirrored to the other. Assuming I don't bottleneck the channel to much. But I am not sure how to do this with SAM (is it possible with SAM ?) or using lvcreate. In lvcreate I read with interest about Extent Based Mirrored Stripes but am not quite sure how to calculate or setup the number of extents. Would EBMS do close to what I want ?

I am looking for advice and experience before I change the config. I have done database performance tests on the current config. so am willing to try other configs. and see. The system is not in production yet, but soon will be.

Thanks, and I would appreciate any help that can be provided.

Rob.

[Steven Sim Kok Leong · Accepted solution]

Hi,

I believe this document which provides the step-by-step instructions for Distributed Allocation Policy will help:

http://us-support3.external.hp.com/cki/bin/doc.pl/sid=9e72a8e417fefb0080/screen=ckiDisplayDocument?docId=200000047804885

Hope this helps. Regards.

Steven Sim Kok Leong

[Patrick Wallek]

Since you are using mirroring, you can't use true striping. You'll have to use Distributed allocation to get "striping" with mirroring.

To create a mirrored, distributed stiped lvol, the following command will work:

# lvcreate -D y -m 1 -L 65000 -s g -n lvol_name vg_name

Check out the lvcreate man page for more details on the above command.