topic Re: Adding drives to EVA 4400 in Disk Enclosures

Adding drives to EVA 4400

JLG2 — Mon, 02 Nov 2009 20:21:54 GMT

I am adding 16- 300GB fibre connected drives to an EVA 4000 with 32- 146GB drives. I have read that it is not recommended that you mix drive sizes in a disk group. I understand why this is the case, but I have a few questions. If I add these drives to my current disk group, how will that affect performance compared to the current configuration of 32 drives. (Would the additional spindles help overall performance even though the larger drives would be hit harder?) How many drives would I add at a time? (They are already installed physically and are listed as ungrouped.) Finally, I would like to change my drive failure protection from double to single. Any advice on that? (Before or after I add the drives?)

Re: Adding drives to EVA 4400

IBaltay — Mon, 02 Nov 2009 20:34:22 GMT

Hi,
the mixture of the disks is allowed but not recommended from the performance point of view:
http://h20195.www2.hp.com/V2/GetDocument.aspx?docname=4AA2-0914ENW&cc=us&lc=en&jumpid=reg_R1002_USEN

it is a good practice to group 8 physical disks to create one RSS (8 phys. disks by default)

the failure protection is kept on the DG level, so after the disk addition or a new 300GB DG creation, you can online change the config of the disk protection. If you go to the mixture it will reserve 2 bigger disks (2x300GB) in the mixed DG

Re: Adding drives to EVA 4400

Amol Garge — Mon, 02 Nov 2009 20:36:00 GMT

Why do you want to waste the disk space? Its like eating half apples and throwing the rest.
You'll be wasting 4.8TB!! Create a new host group instead with 16 drives. Add more drives as and when you have them.

Adding spindles does not always increase the performance, you need to consider other variables involved too.

If you want to add drives, add one at a time or the controller will sleep.

I would strongly suggest not to go for this setup.

Re: Adding drives to EVA 4400

Håkan Persson_1 — Tue, 03 Nov 2009 08:37:18 GMT

He won't waste 4,8TB. The EVA will use all of the space on the drive, and thats a bit of the problem. Since it will try to keep the same amount of data on the drives in percent, the 300GB drives will have twice the amount of data compared to the 146GB (roughly) and because of this it will get more of the I/Os and the possibilty of a bottleneck/hotspot.

Re: Adding drives to EVA 4400

Víctor Cespón — Tue, 03 Nov 2009 09:13:38 GMT

Amol Garge & HÃ¥kan Persson, neither of you is correct. The 300 GB drives will not be used to 100% not to 50% only. The EVA will try to write as much data as possible to the disks without losing RAID redundancy. The space available depends on the amount of VRAID 0 and VRAID 5 disks, and how RSS end up.

Now that you have the disks inserted and running, add them to the disk group all at the same time. This way you'll avoid doing several levelings one after another, and the EVA will know how many disks there will be, so it can think about how to arrange the RSSs.

The disk failure protection = double is not needed on an EVA4000 unless it's in a very difficult to reach place and you do not have spare disks available or cannot get one in a few hours.

Regarding performance, the 300 GB disks will have more load on average, but you'll have more spindles to spread the total, so in the end, each disk has less load than before.

Re: Adding drives to EVA 4400

JLG2 — Thu, 05 Nov 2009 15:08:11 GMT

Thanks to all who answered my questions. I've added the disks successfully and changed the drive failure protection to single.