1 Nickel

## RAID 10 on 8 disks (4+4)

Hello,

I have some questions regarding RAID 10 and how does it work. your help is really appreciated

- The expression "RAID 1/0" does it mean RAID 10 or it may refer to another RAID level like RAID 1 ?

- The minimum number of disks for RAID 1 ? ( Two disks, please confirm)

- The minimum number of disks for RAID 1/0 ? ( Four disks, please confirm)

- Can i create a storage pool only contains 2 disks with RAID 1/0 when we use the Unisphere to create new storage pool?

-  RAID 1/0 has a preference of 4+4 disk but how data will distributed ove 8 disks , is it like the same distribution over 6 disks with additional RAID 1 set.

Labels (1)
• ### VNX

Tags (1)
1 Solution

Accepted Solutions
3 Silver

## Re: RAID 10 on 8 disks (4+4)

Yes, that's my understanding. It's the only way I've known R1/0 to be constructed.

Also, I recall a procedure referred to when I've created RAID 1/0 Groups in the past which showed the correct way to select the disks in order to determine the Primary & Secondary disks in each 'span'. ( There was no tertiary etc).

7 Replies
3 Silver

## Re: RAID 10 on 8 disks (4+4)

Hello,

RAID 10 & 1/0 are the same

Minimum drive count for RAID 1 is 2. On VNX if you create a RAID 1/0 pool of only 2 disks, it really is only RAID 1 at that point as there is only a single mirror pair and thus no striping of pairs. It will not be displayed as RAID 1 though as expansion will then see mirror pairs get striped.

Minimum for actual RAID 1/0 is 4 disks, minimum recommended (for best practice) is 8 (4+4).

You can create a Storage Pool with only 2 disks, that will display as RAID 1/0 but will only really be RAID 1 unless it's expanded.

If you create a 4+4 RAID 1/0 I think the underlying disk groups will be 4 x (1+1) mirrors that will then be striped. In other parlance, each (1+1) group is a span.

1 Nickel

## Re: RAID 10 on 8 disks (4+4)

thanks a million Brett.

So we can create a pool with two disks and if we choose RAID 1/0 the storage will treat these disks as a single mirror set.

in case we expand the pool by adding two additional disk , here the storage will treat the new set as a strip for the mirror set.however if the the first set is almost full, will the storage redistribute the data blocks over the four disks ( the old pair and the new one) or will it  write the new data on the new pair without touching the old pair.

I think you are talking about nested RAID, and what you described in your previous comment is RAID 100 . like the diagram below :

3 Silver

## Re: RAID 10 on 8 disks (4+4)

Yes, when you expand a pool, the data is rebalanced/re-located across the existing and new disks.

and no, I wasn't referring to nested at all, that would require striping RAID 10 groups together, but maybe I didn't explain myself very well and have ammended it now.

The (4+4) notation seems a little confusing, but I expect the underlying construct is made up of  2 disk mirrors (1+1) that are then striped.

If EMC is different to other R1/0 implementations somehow, maybe someone can provide a reference.

1 Nickel

## Re: RAID 10 on 8 disks (4+4)

Sorry, I misunderstood what you said.

So can we consider a (4+4) RAID 1/0 as a 4 mirror pairs and the data blocks are stripping over these pairs.

R1     R1    R1    R1

(1+1) (1+1) (1+1) (1+1)

I am asking about RAID 10 since I am little bit confused how blocks will be stored .

Thanks

3 Silver

## Re: RAID 10 on 8 disks (4+4)

Yes, that's my understanding. It's the only way I've known R1/0 to be constructed.

Also, I recall a procedure referred to when I've created RAID 1/0 Groups in the past which showed the correct way to select the disks in order to determine the Primary & Secondary disks in each 'span'. ( There was no tertiary etc).

1 Nickel

## Re: RAID 10 on 8 disks (4+4)

thank you for sharing such information.

4 Ruthenium