How to Setup RAID 5

[Nago]

Greetings fellows,
Kindly direct me on how to setup RAID5 from scratch on HP 9000 K-class server. That is , if am faced with a number of disks, how do i get started .
Thanks for your response.

[Steven E. Protter]

Quick way.

This thread contains instructions.
http://forums.itrc.hp.com/cm/QuestionAnswer/1,,0x1f26b941255cd71190080090279cd0f9,00.html


sam

disks etc

You should actually be able to set up software RAID 5 striping in there.

One thing should be carefully known. You can't do raid 1+0 striping and mirroring with LVM. The posts I've read for this clearly indicate that.

If you have X Windows, there is something called Veritas Enterprise Administrator, which might provide you the ability to do this on vxvm volumes.

SEP

[Tim Adamson_1]

An addendum to SEP's post above.

If you have HP MirrorDisk/UX you can actually have extent based mirrored stripes. The lvcreate(1M) man page says how to set this up (refer to the -D option).

Be aware the smallest stripe size is 1Mb and with the capacity of todays disks, you wont be able to use a 1Mb stripe size as the VGRA will be too small. Therefore, the stripe size will have to be a minimum of 4Mb.



Tim

[Bill Hassell]

RAID 5 is different than mirroring and striping. It is a collection of disks (like 5) with one reserved as a parity disk. Data is then written across all the disks in such a way that with the loss of any one disk (including the parity disk), the information can be reconstructed error free. As you might expect, this is very costly in CPU time since every write operation must include computation of the contents for each of the disks.

LVM provides no RAID 5 capability. If you are running HP-UX 11.11, you can use VxVM to create a RAID 5 collection of disks. VxVM has a fairly steep learning curve compared to LVM. The K-class box is pretty slow for this task so expect to see as much as a 20% performance penalty for writes to the RAID 5 collection. These performance penalties are the main reason that RAID 5 is usually implemented in hardware such as a disk array controller.

[Sridhar Bhaskarla]

Hi,

As indicated, RAID5 - striping with parity is not possible with LVM.

You can do either striping or mirroring with LVM. Striping+Mirroring is not possible with LVM either. At the best you can do "Extent based mirroring". But here the stripe size is equal to the extent size which may not provide extensive benefits.

-Sri

[Dave Wherry]

On the newer HP servers there is an HBA available that will do Raid 5. Nothing I know of for a K class system.
Usually, Raid 5 is accomplished on a disk array. Then it happens on the back end and the server really does not know about the Raid level. It just looks like a disk to the server and there is no load on theserver because the array handles it. As Bill said, you don't want to do Raid 5 with JBOD.