Striping across 2 Autoraids (12H) ?

[Lothar Krueler]

Hi there,
last weekend i reconfigured our 12H using 2 striped LUNs each VG (a good tip from A. Clay Stephenson). Performance is nearly 20% better during backup. Watching diskactivity using glance i found one application causing heavy traffic on the 12H. I've got a second 12H i still have to configure in the same Cluster, conneted to the same nodes. What do you think about creating a VG striping 2 LUNs on the 1st 12H and 2 LUNs on the 2nd 12H ?

Thanks in advance
Lothar

[Vincent Farrugia]

Hello,

I think you cannot stripe across 2 AutoRAIDs in the sense of striping across 24 disks. Although you can connect 2 AutoRAIDs in the same SCSI chain, they will be addressed as seperate machines, not one.

You can create a second dual LUN on the second AutoRAID though, providing a mirror to the second AutoRAID.

HTH,
Vince

[Lothar Krueler]

Thank you Vince,
where is my fault? I thought, I could vgextend an existigng VG containing 2 logical Disks on 12H#1 with 2 logical disks LUN on 12H#2. The i would create (with SAM) one or more LV in that VG with 4 stripes each ?

Lothar

[Vincent Farrugia]

Hi again,

You could create another lun on the AutoRAID #2 and then vgextend the lun on the first AutoRAID to the second, sure.

I didn't understand the 4 stripes each thing though. Can you specify a bit more?

[Lothar Krueler]

Hi Vince,
the 12Hs have 2 controllers each. The Idea is using both controllers best as possible.
Therefore i create 2 LUNs each VG, 1st with prim.controller X and altern.controller Y, 2nd with prim.controller Y and alternate X. Striping across this 2 LUNs increases performance. Striping across more LUNs on the same 12H has no effect in performance, because the same controllers would be used. Increasing the amount of controllers in a 12H to more than 2 is not possible. But for reducing the traffic on each controller i have to add controllers. So the idea is adding controllers by using additional LUNs on another 12H. In my environment i cannot test this, because the 1st 12H has no more free LUNs and the 2nd isn't integrated yet.

Lothar

[Vincent Farrugia]

Hi again,

Yes you can do that I think. You need an additional 2 controllers in your host for maximum high availibility.

HTH,
Vince

[Insu Kim]

Configuring the disk array in that manner will give you better performance.

[Insu Kim]

Rules for getting better performance from hardware standpoint,

1. Amount of available RAID 0/1.
The more RAID 0/1 space available, the better the disk array performance.
Enabling Hot spare will allow you to have more RAID 0/1 space.
2. Proper disk module installation.
Installing the disk modules in the correct slots in the enclosure distributes the disks across the internal SCSI busses and balances the I/O load properly. Disk modules should be installed from left-to-right, top-to-bottom.
3. Keep the disk capacity small ??? Having twelve disks with smaller capacities will improve the performance as compared to having twelve disks with larger capacities.

[Steve Labar]

I don't think implementing a second 12H will provide the results you are looking for. Increasing RAID 0/1 space will increase performance inside the RAID. However, to increase RAID 0/1 space you need to increase unallocated space. Which means disk space not assigned to a LUN. I haven't run multiple RAIDs in tandem, but I don't think the second RAID would get used in the VG until the first RAID is full. Depending on how many LVOLs you are using, you might be able to pvmove an LVOL to the second array, but as files are modified, I wouldn't guarantee they would stay there.

Good Luck.

Steve

[Lothar Krueler]

Thanks for your thoughts,
i hoped that anyone would have expieriences in striping across raids.
But your answers make think it's worth a try.

Insu, your 3rd rule i cannot beleive in, 12 disks are 12 disks, but i think 12*18GB are faster than 6*36GB. Is that what you meant ?

Steve, i think, if STRIPE-configuration across several raids is possible, then data really MUST be distributed to the several raids in parallel and not in sequence, that's the sense of striping.

Thanks again
Lothar