4

I have an HP Smart Array P400i raid controller, with 6 disks, working in a RAID 1+0. This is what it looks like:

     Mirror Group 0:
        physicaldrive 1I:1:1 (port 1I:box 1:bay 1, SAS, 72 GB, OK)
        physicaldrive 1I:1:2 (port 1I:box 1:bay 2, SAS, 72 GB, OK)
        physicaldrive 1I:1:3 (port 1I:box 1:bay 3, SAS, 72 GB, OK)
     Mirror Group 1:
        physicaldrive 1I:1:4 (port 1I:box 1:bay 4, SAS, 72 GB, OK)
        physicaldrive 2I:1:5 (port 2I:box 1:bay 5, SAS, 72 GB, OK)
        physicaldrive 2I:1:6 (port 2I:box 1:bay 6, SAS, 72 GB, OK)

If my understanding is correct, drives 1 and 2 could fail, and the RAID would still be ok.

This doesn't seem right to me, I was thinking a RAID 1+0, with 6 drives should look like this:

     Mirror Group 0:
        physicaldrive 1I:1:1 (port 1I:box 1:bay 1, SAS, 72 GB, OK)
        physicaldrive 1I:1:2 (port 1I:box 1:bay 2, SAS, 72 GB, OK)
     Mirror Group 1:
        physicaldrive 1I:1:3 (port 1I:box 1:bay 3, SAS, 72 GB, OK)
        physicaldrive 1I:1:4 (port 1I:box 1:bay 4, SAS, 72 GB, OK)
     Mirror Group 2:
        physicaldrive 2I:1:5 (port 2I:box 1:bay 5, SAS, 72 GB, OK)
        physicaldrive 2I:1:6 (port 2I:box 1:bay 6, SAS, 72 GB, OK)

The data would be striped across the 3 mirrored pairs.

Are both configurations possible, or just the first?

2

You do not have a choice on the drive arrangement/pairs.

In that arrangement HP Smart Array controllers split the disks as such:

physicaldrive 1I:1:1 pairs to physicaldrive 1I:1:4 
physicaldrive 1I:1:2 pairs to physicaldrive 2I:1:5
physicaldrive 1I:1:3 pairs to physicaldrive 2I:1:6 

RAID 1+0 == RAID 1 pairs, striped (RAID 0) together...

You can lose ONE disk from each of the pairings listed above. Or, one drive from each "Mirror Group".

Also: What are the different widely used RAID levels and when should I consider them?

  • 1
    Shouldn't you be able to lose every single disk from a mirror group as long as the other mirror group is intact or am I missing something about the HP-specific terminology here. – MDMarra Apr 20 '12 at 16:43
  • Yes, you can lose all of the disks in single mirror group as long as the other mirror group is healthy. In HP terminology, the Mirror Group 0 and 1 just represent the division of one side of the mirror from the other. – ewwhite Apr 20 '12 at 16:46
  • 2
    The output from the controller seems counter intuitive to me. But you're right. I killed drive 1, 2, and 3, and everything is still fine. So 1 is a mirror of 4, 2 is a mirror of 5, and 3 is a mirror of 6. That's the setup I want. – Matt Apr 20 '12 at 16:50
0

Both configurations are probably possible but using the first seems riskier.

The first situation leaves you with, depending on implementation in the controller, possibly a longer rebuild (it may have to read all three drives of the stripe to rebuild the mirror made of three drives) as well as if you lose a drive out of each stripe set the array fails.

The second provides faster rebuild (only rebuild a single drive to its mirror) as well as better protection 1 drive of each mirror can fail before the array is no longer available.

  • This is still RAID 1+0. The HP controller pairs a drive from one Mirror Group to a drive from the other Mirror Group. – ewwhite Apr 20 '12 at 16:22

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.