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MSA 2040 expansion Virtual Pool

 
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ToreJ
Occasional Contributor

MSA 2040 expansion Virtual Pool

Hi.

I've got a MSA 2040 with 24 disks, and Virtual Pools: A, B

In Virtual Pool A, I've got 8 disks in one Raid10 Diskgroup, and one virtual volume.

In Virtual Pool B, I've got two Virtual Diskgropus in Raid 5. (7 disks + 9 disks), and One Virtual Volume.

There is also two disks as global spares.

 

We need more space now, and a new large separate volume mapped to another server.

The data from volume in Pool A, has been moved to the volume in Pool B for the moment, so Volume A can be cleared..

I've also got a new diskshelf available now with 10 more disks.

My first thought was to set up these 10 disks in one Raid6 diskgroup, and add this to Pool A.

But I've read It is not best practice to mix different Raid diskgroups in the same Virtual Pool? 

Should I rather, delete the Raid 10 Diskgroup, and use these 8 disks in a new Raid6 diskgroup?Theat will give me thow Raid6 diskgroups in the same pool. 8 disks + 10 disk.

Would the Raid10 diskgroup together with the Raid6 diskgroup in Pool A increase the Write speed compared to two Raid6 diskgroups?

The MSA is used in a two node Hyper-V Cluster, with some virtual servers:

(RDS, SQL, Exchange, FILE, Print)

Tore J

4 REPLIES 4
HPSDMike
HPE Pro

Re: MSA 2040 expansion Virtual Pool

Hello,

With pools, or any type of striping, it is best practice to keep the same disk type, RAID type, and set size. The reason is because you can have inconsistent performance without. Whether that inconsistent performance is noticeable in your particular environment is not something I can determine but it is possible. The reason is because your worst case performance will always be the lowest common denominator. Say you install 20 x 300GB 15k drives in RAID1 VDISKS. Next, you add 4 x 2.4TB 10K drives in a RAID5. Some, or all (if very small volume), of a given volumes data could live on those 4 x 2.4TB disks and take on the performance characteristics of it. Also, rebalancing is done by the amount of free space available on the drive. So, during a rebalance, a ton of data is going to get moved to those large drives potentially creating some undesired hot spots. I'm giving an extreme example to prove my point. Minor deviations in drive type/sizes or RAID set characteristics can also go completely unnoticed. 

Now, onto your real question. I think you have to ask yourself why you chose RAID10 to begin with. If you need the increased write performance that RAID10 can provide (and can tolerate the 50% space reduction) then go with RAID10 on the new disk group, add it to the pool, and call it a day. 

If you want as much space as you can get (while having really good data protection) then wipe away what you have in Pool A and create your two RAID6 sets as you mentioned. You don't mention your existing, and new, disk sizes, but if they are the same then I don't think you're going to see a huge issue with the two RAID set sizes. The big thing is to try and stick to the "Power of 2" rule for best performance. This is where the number of data drives is a power of 2, but less than 16 (since MSA can't have more than 16 disks in a VDISK). So, you would do yourself a huge favor by purchasing two more disks and creating two RAID6 sets of 10. You'll have WAY more disk space than RAID10, be meeting the Power of 2 rule, and have very good data protection with double parity drives. I would not mix RAID10 and RAID6 in the same pool. It makes no logical sense and will cause performance inconsistencies. Choose one and go with it. It sounds like you have some flexibility to move data around so maybe you could try RAID6 and, if you didn't like the performance, you could move everything off and recreate on RAID10. 

 



I work for HPE. The comments in this post are my own and do not represent an official reply from the company. No warranty or guarantees of any kind are expressed in my reply.

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ToreJ
Occasional Contributor

Re: MSA 2040 expansion Virtual Pool

ok. Thanks.

The disks are all the same. 15k 300GB.

The reason I created a Raid 10 diskgroup at the beginng was to have the best perfomance on SQL end Exchange transactions, but I'm not sure if it is noticable here in this setting.

I think I'll go with your advise and create two Raid6 diskgroups then wtih the 8 + 10 disks. I need the space...

If I am going to add two more disks to create to even dsikgroups with 10 disk each, I will have to use the two Global spares disk in the same diskshelf. If not the Diskgroup will span over two diskshelf, and this is not recomended..

But I can ask the customer to buy two more disk if it will be reasonable

HPSDMike
HPE Pro
Solution

Re: MSA 2040 expansion Virtual Pool

Spanning shelves in a disk group is fine. In fact; as soon as the first drive fails, and your spare takes over, then you'll have caused it to span shelves there. I would see if they are willing to buy two more disks; if they are then do one of two things:

1) Create your 2 x ten disk sets now (using your spares) but be real careful to keep an eye on your RAID5 sets and get failed drives replaced immediately until you have your spares back online

2) Since you are moving to RAID6, you might have enough space in your ten disk RAID6 set for now so you can create one 10 disk set. Then, when you get your other two disks in, create your additional ten disk set and add it to the pool (this can be done online). You'll want to avoid trying to go from an 8 to 10 disk set later.

If they are not then create your 10 disk and 8 disk set but I guarantee you that your performance will not be optimal. You'd be better creating a ten disk set and a six disk set in that case so you can stick to "power of 2".


I work for HPE. The comments in this post are my own and do not represent an official reply from the company. No warranty or guarantees of any kind are expressed in my reply.

Accept or Kudo

ToreJ
Occasional Contributor

Re: MSA 2040 expansion Virtual Pool

ok. Thanks for your advices! 

I'll advise the customer to buy two more disks then, and create one diskgroup now with the 10 disks, and the other diskgroup when we got the disks.

Best regards

Tore