topic Re: HPUX 11i Raid 5 in Operating System - HP-UX

HPUX 11i Raid 5

Douglass Anderson — Wed, 12 Sep 2007 10:20:10 GMT

I have four 35 GB disks in one disk bay.

HPUX 11i V1 - with HPUX Mirror app Installed.

How can I set them up in RAID5 ?

Re: HPUX 11i Raid 5

Tom Danzig — Wed, 12 Sep 2007 10:22:12 GMT

You can't. MirrorDisk only mirrors (i.e. RAID 1) in software.

Re: HPUX 11i Raid 5

Patrick Wallek — Wed, 12 Sep 2007 10:22:27 GMT

You can't.

The MirrorDisk/UX software allows you to mirror (Raid 1) only. There is no software support for RAID 5 with HP-UX LVM.

I **THINK** that you can do software raid 5 if you convert to the full version of Veritas Volume Manager (VXVM) software. I'm not completely certain though.

Re: HPUX 11i Raid 5

Bill Hassell — Wed, 12 Sep 2007 11:13:10 GMT

RAID 5 is only useful when it is run by a dedicated controller. If you buy the Advanced VxVM (Veritas Volume Manager), you can setup RAID 5 but be aware that like any RAID 5 arrangement, there is a *LOT* of CPU required to spread the bytes across multiple disks and to compute associated parity codes. You will have significantly lower performance with RAID 5 running inside HP-UX compared to RAID 1 (simple mirroring). Also, it will be tough to setup RAID 5 with just 4 disks. The minimum (not recommended though) is 3 disks with 5 disks being the most common method.

Re: HPUX 11i Raid 5

Hein van den Heuvel — Wed, 12 Sep 2007 12:13:12 GMT

Are those disk in a bay directly connected to an HBA on the system (local disks) or through an intermediate controller (EVA, Smartarray, EMC,..)?

I'll assume, with the other readers, that it is directly connected and then the answer would be NO.

To expand a little on Bill's reply:

>> RAID 5 is only useful when it is run by a dedicated controller.

Because it really needs a battery backed-up write-back cache to get decend performance

>> If you buy the Advanced VxVM (Veritas Volume Manager), you can setup RAID 5 but be aware that like any RAID 5 arrangement, there is a *LOT* of CPU required to spread the bytes across multiple disks and to compute associated parity codes.

I would worry more about the IO required than the CPU needed, but the end result is the same: Too costly. For every write to a raid-5 disk the system needs to 1) read-old-data (probably already in cache) 2) read-old-parity 3) write new-data 4) write new parity. 1 IO turns into 4, and the read-old-parity is likely to be a non-cached, slow IO.

>> it will be tough to setup RAID 5 with just 4 disks. The minimum (not recommended though) is 3 disks with 5 disks being the most common method.

With 4 drive raid 5 you get 3 drives worth of data and a lot of hassle (hassell?).
Change to raid-1 and performance get's better and you still have 2 out of 4 drivers for data. 50% less, bit not too bad perhaps.

fwiw,
Hein.

Re: HPUX 11i Raid 5

Douglass Anderson — Wed, 12 Sep 2007 12:36:43 GMT

it is attache through a 1200 Disk bay.

Re: HPUX 11i Raid 5

Douglass Anderson — Wed, 12 Sep 2007 12:37:14 GMT

it is attached SCSI through a 1200 Disk bay.

Re: HPUX 11i Raid 5

Torsten. — Wed, 12 Sep 2007 13:46:21 GMT

Don't know what a "1200 Disk bay" is, but you may consider to use a hardware RAID controller.

Re: HPUX 11i Raid 5

Douglass Anderson — Thu, 13 Sep 2007 09:32:45 GMT

disk bat 2100 does support Raid Controller. I will check with HP on ordering one.