VA7400 config

[jh_yang]

Hi,
If I wanna use RAID 0+1 for RG1 and RG2, I put 7 disks in RG1 and 6 disks in RG1, then use other 2 disks as hotswap for each RG. Is this configuration make sense?
I just wonder if RAID 0+1 is used, is it possible to put 7 disks in one RG? If yes, how the 0+1 implement? 1,3,5 for RAID 0. 2,4,6 for mirror? how about disk 7?

Best Regards
David

[Vincent Farrugia]

Hello,

Yes, it makes sense. RG1 uses all odd-numbered harddisks, RG2 uses all even-numbered harddisks. Each RG has to have a hotswap disk each, so yes it makes sense.

RAID 0+1 on odd-numbered disks works in this way:

1 mirrored with 2, 3 mirrored with 4, 5 mirrored with 6, 7 mirrored with 1, 2 mirrored with 3 etc. These are all stripes.

HTH,
Vince

[Roger_22]

Remember, the VA does not have a traditional spare disk implementation. The VA implements Active Hot Spare. All the disks are used to store data, but an equivalent capacity to the largest (or two largest) disk(s) in an RG are distributed and reserved across all the disks in the RG. In the event of a disk failure, the data on the failed disk can be recreated on this reserved space.

Active Hot Spare gives you a performance advantage over traditional reserved spare implementations, particularly in small configurations. More disks, more performance. It also eliminates the chance that the spare disk has gone bad without notification.

[Vincent Fleming]

The reason it's called a Virtual Array is that the RAID is implemented as "virtual RAID"... which means that when it does mirroring, it does not mirror the drives in the classic sense where every byte on one drive is copied to another...

What is does has the same effect, but is done at a different level. It's mirrored at the *block* level. Every block of a LUN is copied to 2 drives in the array.

So, the drives themselves are not paired, but the data on the array is still mirrored.

Because of this, a RAID 0/1 configuration can use an odd number of drives... and it does.

Here's an example of how it works:

Let's assume we have 5 drives in the RG...
Block 1 is mirrored on drives 1 and 2 of the RG. Block 2 is mirrored on drives 3 and 4. Block 3 is mirrored on drives 5 and 1. Block 4 is on drives 2 and 3.

It wraps around. You're still protected against drive failures.

So, go ahead and use however many drives as you like. It doesn't matter.

Good luck!