snapclone or mirrorclone

[Steven Clementi · Accepted solution]

You guys are missing the fact that Ben's main concern is that when grouping the new disks, his users might notice some performance degradation while the DG levels.

Personally, I don't think the users will see any difference in performance. Sure, there will be some difference... but I think it is negligable compared to the performance cut they might notice after you move Virtual disks to a DG with 40 disks vs. 73 or 95 disks.

Even then they would have to be a high performance user with a pretty high i/o profile on the EVA to notice any really big change.


The short story is, I think you would be fine grouping the 40 disks in with one of your other groups, or both (splitting them to give both groups space (and yes.. trying to keep with the multiple of 8 best practice)). Even if you started 6pm Friday and the leveling was well along it's way by monday morning, I think the price you'd pay is less then if you had a 3rd DG.

Facts...

Protection levels is PER Disk Group. You will lose additional raw space by creating a 3rd DG.

"partial RSS's consisting of 7 and 9 drives will cause a performance issue." - I never actually seen any performance issues when there is a RSS of less/more than 8. It simply means that redundancy is not optimal in 1 set of disks.

"Best thing for you to do is:" - might not be to combine all of your disks into 1 Disk Group. Lot's of reasoning goes into the decesion to have a single or multiple disk groups... and we do not know how your EVA came to have 2 Disk Groups.

Different applications require different i/o performance, internal politics sometimes plays a role in the decision to have one or multiple DG's, etc.

It is very easy to state the Best Practice(s).


Steven

[ben horan]

Thanks guys - especially Steven. After your comments I think we will go for integrating the expansion cabinets 40 disks into the existing disk groups. We will also aim to make the disk numbers divisible by 8 in the DGs. We need to stay with the 2 DG's as one is a very sensitive email application and mangement like it to be in its own DG.

Is there any best practise as to how many disks we can add at one time? i.e. is 32 in one go okay?

[IBaltay]

>Is there any best practise as to how many >disks we can add at one time? i.e. is 32 in >one go okay?


HDD installation

HP recommends to install (not group) a maximum of 4 HDD at one time. The procedure is the following:
1. insert not more then 4 physical disks
2. wait until the activity indicator on each inserted drive becomes solid green and remains solid for 10 seconds
3. you can proceed with 4 other disks until 32

HDD grouping to the DGs
the best is to check the original RSS layout
if you have any RSS with 6 members i would first saturate those hungry ones and then add the disks in the groups of 8 to have full vertical layout, which should be fairly easy with 18 enclosures

[Uwe Zessin]

> HP recommends to install (not group) a maximum of 4 HDD at one time.

I strongly recommend to install one disk drive at a time and wait until it has been properly recognized in Command View EVA. Yes, this takes a lot of time, but I still see EVAs with duplicate disk drive names which is caused by CV-EVA.

[ben horan]

We will add disks to the expansion cabinet one at a time to be safe.

We do actually have 2 disks with the same name in another disk group, is this okay? Is there any fix required?

[IBaltay]

Each disk has its own unique wwn so the logical name should not be a problem

[Uwe Zessin]

It is a problem, because one of the disks with a publicate name is not completely processed by CV-EVA. For example
- it is not included in the disk counts
- last time I was searching for it, the icon did not appear in the disk group hierarchy

I find it very confusing if an incorrect number of disk drives shown ;-)

[Uwe Zessin]

> Is there any fix required?

Sorry, Ben, missed the question.
In that case I simply give the visible disk a different name within CV-EVA. After a refresh / new discovery, the view should be correcct.