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Ungrouping disks on EVA3000

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Robert Campbell
Occasional Contributor

Ungrouping disks on EVA3000

I am running an EVA3000 with 10 disk units. Currently all the units belong to the default group. We are adding 6 units to the EVA. I would like to take two of the units from the default and create a new group. From my research it appears that I can do this by ungrouping the two drives and when I ungroup the data will be spread over the remaining drives. I do have plenty of disk space. Is it possible to ungroup drives from an active group? Also, are there any actions that need to be taken with Secure Path when this is done? I've only been using the EVA for a couple of months now so still unsure of what I can do and can't do.

Thanks

6 REPLIES
Steven Clementi
Honored Contributor
Solution

Re: Ungrouping disks on EVA3000

Robert:

As long as you have space to cover the loss of 2 disks, you should be able to just ungroup them. You do not need to do anything with Secure Path. You can do it while it is active, though for better performance/quicker leveling, do it when there is not alot of I/O (nighttime/weekend/etc).

Once the disks are removed, you should be able to immediatelly create the new disk group as the old one is leveling, but you might want to wait a little while just to give it some tie to get started (or finish up).

One thing to consider is your protection level. If your at 2, you effectively cut your raw storage in half with only 8 disks. If your at 1, you cut it by 25%.


Steven
Steven Clementi
HP Master ASE, Storage and Clustering
MCSE (NT 4.0, W2K, W2K3)
VCP (ESX2, Vi3, vSphere4, vSphere5)
RHCE
NPP3 (Nutanix Platform Professional)
Robert Campbell
Occasional Contributor

Re: Ungrouping disks on EVA3000

Thanks Steven for your reply. I would like to ask for some clarification on the protection level. I found the "Disk Failure Protection" under the group. It is "single". I believe this is what you are referring to the as the protection level. I have all my virtual disks set up in raid 5 and have 284gb available for raid 5. If I ungroup two 72gb drives, would that create a potential problem?
Uwe Zessin
Honored Contributor

Re: Ungrouping disks on EVA3000

Yes. 'failure protection' or 'protection level' or variations are a bit misleading, because the mechanism just reserves disk space equally distributed over all disks in the group instead of a dedicated spare disk - it has nothing to do with a VRAID-level.

You calculation sounds OK. So you have about 284*1.25 = 355 GigaBytes raw space free.
355 - 2*72 = about 211 GigaBytes left


Remember that all virtual disks in a disk group are spread over all physical disk drives. By using two disk groups, you will create two different I/O domains. You have now reduced that to 8 physical disks. It is possible that the disks in one disk group are working very heavy while those in the other group are idle.
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Steven Clementi
Honored Contributor

Re: Ungrouping disks on EVA3000

With that said, the HP Recomendation is to create one disk group with all your disks, unless there is an absolute necessity to split them up. I consider different size disks a necessity, but it really isn't.

16 spindles vs. 8 spindles....


Also, the "sweet spot" for the EVA was calculated at about 59 drives. (I could be a bit off). This means that as you reach 59 disks in a group, the performance gain is slightly higher than par. After the 60ths disk, the performance gain is not so good.

All disks in one group with single protection would actually yield more available storage than 2 8-disk groups with single protection

Steven
Steven Clementi
HP Master ASE, Storage and Clustering
MCSE (NT 4.0, W2K, W2K3)
VCP (ESX2, Vi3, vSphere4, vSphere5)
RHCE
NPP3 (Nutanix Platform Professional)
Robert Campbell
Occasional Contributor

Re: Ungrouping disks on EVA3000

Thanks Steve and Uwe for the great information. It really helped.
Tom O'Toole
Respected Contributor

Re: Ungrouping disks on EVA3000

When you ungroup the drives, you may want to do them one at a time. We have ungrouped a bunch of drives 'in the background' simultaneously - the controllers did not handle this well - they rebooted. But this was with 3010 I think.
Can you imagine if we used PCs to manage our enterprise systems? ... oops.