topic Re: Question on VA7100 in Disk Enclosures

Question on VA7100

Mike_305 — Tue, 28 Sep 2004 17:18:12 GMT

Hi,

On VA7100 I have useable space of 498 GB with raid 1+0 configuration. My question is; does it make any performance difference on VA, how many numbers of LUN’s I have.

What I am trying to say is if I create 10GB size of 50 LUN’s v/s 25GB of 20 LUN’s, or a 1 LUN of 500GB.

Does performance get affected by how many LUN’s you have on the system?

In the old days on 12H array the lesser number of LUN’s gave better performance.

Thank

Re: Question on VA7100

Sridhar Bhaskarla — Tue, 28 Sep 2004 17:44:34 GMT

Hi Mike,

I am one of those SysAdmins who believe that I get better performance with reasonable number of smaller LUNs than few big LUNs. This is because system can only queue certain number of requests and that number doesn't change with the size of the LUN. You will have to modify the 'scsi queue depth' kernel parameter in order to pump more requests.

I would go for either 16x 28 GB Luns or at the max 8x 56 GB LUNs for your configuration. Depending on the total storage I am going to have, I change the LUN size keeping in view the performance and manageability.

-Sri

Re: Question on VA7100

Steven E. Protter — Tue, 28 Sep 2004 17:54:03 GMT

Disk performance comes from a number of factors:

1) How many disks the LUN is striped across. The rule of thumb is more disks better performance. Reality has sometimes broken that rule with us.
2) Raid method - You are going to get better performance with raid 1 mirroring, lvextend -m 1 ... than with Raid 5 striping.

Of course Raid 1 costs you a lot of disk space because there are two distinct copies of everything.

In practice I like to have luns have a distinct purpose. More smaller ones (as Sridar notes) work better. I have an 8 Lun per fiber card limit which you do not face with HP equipment.

I like a LUN for oracle data.
I like a LUN for oracle index
I like a lun for application executable.

This gets me the most out of the disk presented to me by my disk administrator.

SEP

Re: Question on VA7100

Mike_305 — Tue, 28 Sep 2004 18:08:26 GMT

Hi,

I have VA7100 with the 15 disk 73Gig each, 2 controller with 512MB. VA7100 does not let you create the LUNâ s like JBOD. It gives me one chunk of 500gig space and I create the lun.

What I am trying to find out is, if the smaller size LUNâ s will give me better performance or the large size LUNâ s?

Thank

Re: Question on VA7100

Sridhar Bhaskarla — Tue, 28 Sep 2004 19:01:14 GMT

Mike,

From the storage perspective, it doesn't matter they are smaller or larger as the underlying disk structure is already striped with mirror.

It's only from the system's point of view. When I started in the present company, most of the systems were configured with monsterous LUNs and we never had a day without disk issues. We gradually migrated towards smaller LUNs and took care of how we lay the data and now we rarely have issues.

Again, it doesn't mean that I am suggesting to configure numerous smaller LUNs and make the life miserable. You can carefully carve up LUNs in such a way that the arraygroups are devided according to the type of activity like index, data, sequential, random, mixed etc., so that you will have flexibility on the system. With one or fewer LUNs, you can't control how you access the storage.

-Sri

Re: Question on VA7100

Mike_305 — Tue, 28 Sep 2004 21:33:06 GMT

Since I have only one group to configure my Lun s it looks like it really doesn t matter.

Appreciate your help.

Thanks,

Mike

Re: Question on VA7100

Mike_305 — Tue, 28 Sep 2004 21:34:50 GMT

Thanks