topic HP Smart Array - RAID and Logical Arrays in Disk Enclosures

HP Smart Array - RAID and Logical Arrays

CliveRichardson — Wed, 01 May 2013 07:56:16 GMT

Hopefully a simple answer to what seems to be a fairly simple question...

If, for example, you have a P800 HP Smart Array with 24 disks and a spare and you want to partition a number of database files across drives to maximise I/O performance (the transaction log file is heavy on writes and the other data and index files are heavy on reads), would it be better to:-

a) Use the 24/25 disks to create one SAS Array and three logical drives:-

SAS Array A with spare - 3 Logical drives

     Logical Drive 1 (1200 Gb, RAID 1+0)
     Logical Drive 2 (1200 Gb, RAID 1+0)
     Logical Drive 3 (1200 Gb, RAID 1+0)

b) Use the 24 disks to create three SAS arrays each with one Logical Drive:-

SAS Array A & Logical Drive 1 (1200 Gb, RAID 1+0)
SAS Array B & Logical Drive 1 (1200 Gb, RAID 1+0)
SAS Array C & Logical Drive 1 (1200 Gb, RAID 1+0)

Not sure how the Spare disk fits into Option B?

Anyway, if the objective is to maximize I/O performance, is it Option A or B?
The phrase, 'logical drive'... Does this mean that I/O is partitioned at the logical drive level or does the HP Smart array controller spread the I/O across the SAS Array? If I look at I/O counters (eg. Perfmon on Windows Server), I can see that Logical drives as in Option A seem to be separated completely as one logical drive could have a disk queue and other logical drives on top of the same SAS array will not have a disk queue. What are the prose and cons of Option A and B? Understanding these issues will help me to come up with the right configuration in terms of arrrays and logical drives.

Thanks in advance,

Clive

Re: HP Smart Array - RAID and Logical Arrays

gregersenj — Mon, 06 May 2013 07:07:17 GMT

Have you found an asnswer from any source to your question?

I don't know, wich is faster.

But from a security point of view, I would say option B.

Option A:

All data is on all and the same disks. When you create 3 logical drives on an array, its like when you partition a single disk.

You will have LD 1, at the bottom, LD 2 at the mittle and LD 3 at the top.

In case of a disk failure, LD1 wil be rebuild first, then LD 2 and finally LD 3.

If you suffer from a catastrophic disk failure, all is lost.

/jag

Re: HP Smart Array - RAID and Logical Arrays

Mark Matthews — Wed, 08 May 2013 16:00:12 GMT

I would go with option B.
Or even better, an additional array controller, so you'd have one for the OS and the other for your databases.
You should see a nice performance boost then...

I'd definately configure a spare with all those disks, maybe even two.

A spare can be assigned to multiple arrays / logical drives at the same time so it'll cut in for any disk that fails in any logical drive configured on the same controller.

Thanks
Mark...