Raid levels in a pool

what do you want them to be ?

Raid 6 10+2 comes to mind With that number of drives

But the point is that we would Like get confirmation If EMC Best practises are Best practises or ryles that Cannot be broken.

Doing This by unisphere makes one R6 6+2 and one R6 2+2

It has Been tested

We are hoping that there is a Way around the fixed raid levels In the gui

Jim,

what if you select 6+2R6 , under disks select Manual and select all 12 disks ( i assume you saved some for HS). I would be curious if it would create one private RG (6+2) and then another private RG using the remaining 4 drives.

If you want a RAID 6 (10+2) tier, you could select:  RAID 6 (14+2) and only add/expand 12 drives at a time.  However, from this point on (having deviated from the recommended multiples), the "best practice" for you now would be to expand in increments of 12 so that you always get 10+2 PRG's.

For instance, say you have 24 drives to add to a tier that was created as stated above.  You would expand in two steps of 12 drives each.  Therefore, if you were to view the PRG's (as demonstrated below), you would have the desired: 3x 10+2 PRG's.  Each of the 1GB slices will be coming from consistent size PRG's.  On the other hand you would *not* want to expand in a single step with the 24 drives as you would then have:

1) 10+2 (original)

2) 14+2 (new)

3) 6+2 (new)

Here's a quick summary of the logic behind how the PRG's are created and how to view the PRG's:

Firstly, to view how the private RAID Groups of the pool were created, you can use naviseccli as follows:

navisecccli -h getrg -<engineering password>

In addition to showing the private RAID Groups of the pool, it will also show how the (private) RAID 1 mirrors are setup in FAST Cache so *where appropriate*, for instance, you can verify that for instance the mirrors are separated from the primaries on separate buses or if on the SPS protected vault DAE, they are not separated.  Keep in mind there isn’t a way of interpreting the output of "cache –fast" to determine this.

As for the logic behind how the PRG’s are created when drives aren’t added in the recommended multiples, I’d like to quickly summarize and apologies if this is repeating what you know:

1) From the drives being added, it will try to create as many private RG's of the recommended multiples which are:

(Number of disks / recommended multiple)

RECOMMENDED MULTIPLES

========================
a) VNX OE for Block 32 (Inyo)

(the number of drives are obviously also the selected RAID Group size, but listing for sake of being thorough)

1) RAID 5 (4+1) = 5
2) RAID 5 (8+1) = 9
3) RAID 1/0 (4+4)= 8 (can only add in multiples of 2)
4) RAID 6 (6+2) = 8 (can only add in multiples of 2)
5) RAID 6 (14+2) = 16 (can only add in multiples of 2)

b) VNX OE for Block 31 (Elias)

1) RAID 5 = 5 (4+1)

2) RAID 6 = 8 (6+2)

3) RAID 1/0 = 8 (4+4)

2) From the left over drives, does this meet the minimum requirement for the RAID type?
               
MINIMUM REQUIREMENTS
=======================

a) RAID 5 = 3
b) RAID 1/0 = 2
c) RAID 6 = 4

- If it does, then it will create another private RG from the left over drives

- If it doesn't, then it will distribute amongst the private RG's it calculated in step 1 above

NOTE: the distribution will only be amongst the new candidate private RG's (and *not* existing in the case of pool expansion)

EXAMPLES
=========
So using a quick example, say you add 14 drives and select RAID 6 (6+2):

1) 14 drives / 8 (recommended multiple) = 1 RG with 6 drives left-over
2) Since from the remainder the minimum is met for RAID 6, it will create another 4+2 PRG

Therefore, if you ran the command above, you would see the following PRG’s:

1) 1x RAID 6 (6+2)
2) 1x RAID 6 (4+2)

Now, to mix it up a bit, let’s say you create a new pool (or expand an existing pool) of RAID 6 (6+2) and add 10 drives:

1) 10 drives / 8 (recommended multiple) = 1 RG with 2 drives left-over
2) Since from the remainder the minimum is not met for RAID 6, from the new drives it will create just 1x RAID 6 (8+2)

Inyo RAID 1/0,6 ---> (can only add in multiples of 2)

Does that mean we can only add RAID 1/0,6 in multiples of 16 or 32 disks?

After you asked, I realize now how it can been misinterpreted from what I meant to convey.  It probably would have been worded better as follows:

[...]

a) VNX OE for Block 32 (Inyo)

(the number of drives are obviously also the selected RAID Group size, but listing for sake of being thorough)

1) RAID 5 (4+1) = 5
2) RAID 5 (8+1) = 9
3) RAID 1/0 (4+4)= 8  (can only add an even number of drives)
4) RAID 6 (6+2) = 8  (can only add an even number of drives)
5) RAID 6 (14+2) = 16  (can only add an even number of drives)

[...]

Then this should have also been carried over to the following section as it still applies:

[...]

b) VNX OE for Block 31 (Elias)

1) RAID 5 = 5 (4+1)

2) RAID 6 = 8 (6+2)  (can only add an even number of drives)

3) RAID 1/0 = 8 (4+4)  (can only add an even number of drives)

[...]

Hi Baif,

My comment about "(can only add in multiples of 2)" for both RAID 1/0 and RAID 6 was simply a reminder that regardless of how many drives you add and whether or not you stick with our recommendations when selecting the number of drives, you can't choose an odd number of drives.  In other words, knowing that fundamentally the pool is created from traditional (private) RAID Groups, the same limits apply, and one can't create a (traditional) RAID 1/0 rg with, for example, 5 drives or a (traditional) RAID 6 rg with, for example, 7 drives. 

This comment by itself doesn't at all influence how large the batch of drives you add to a pool other than being an even number.  For RAID 1/0 the multiple of 2 is related to the mirrored pair (PRI and MIR) and for RAID 6 the multiple of 2 is related to the dual-parity.  Having just reread my post, the same comment "(can only add in multiples of 2)" of course applies also to Elias (VNX OE for Block v31) since this was a requirement even before pools were introduced, or rather has always been a requirement with traditional RG's. 

Or did I misunderstand the question?

Chris, thanks for your time of clarification.

Normally I talk to people - you'd better expand the Pools with aliged RAIDs.

You would get a 12+2R6 if you add 14 disks with R6

Anyone measure noticeable performance impact going outside of the recommended multiples?

Also, what would happen if I did something like this for a pool:

Drives available = 15

RAID6 (14+2) -> 14 disk selected

Would the system consider it a completed private RG with those 14 disks?  What about if I add another set of 14 disks later to the pool?

Reasoning I'm asking is that it makes more sense to just till a DAE with 15 NL disks and create from there (DPE is 2.5").

Hi,

I have Pool with RAID1/0(4+4)  which is now full, now I want to expand the pool (all thick luns)

Disks : SAS Flash VP

i have 9 disks available to expand but i want to use only 2 or 4 disks is that fine ?

yes