RAID 0+1 questions

[aoch88]

Hey folks, I am running RAID-0 for some time and would like to explore the options for 0+1 but have some questions:

1. If I have 2 x 1TB disks running RAID0+1 and would like to add another 2 disks in future, do I need to re-format/re-configure the whole array?

2. Does RAID0+1 configuration of the above gives a better read/write speed compared to only RAID-0?

I'd like to partition my disk so that my C:\ would only have 100GB or so while the rest is in D:\ as it'll make my life easier every time I re-install my Vista :)

[SLORider]

This doesn't make sense... RAID 0+1 requires four drives.

[neonblingbling]

Are you talking about Intel Matrix RAID?

[aoch88]

Sorry guys, I used this to calculate:
http://www.ibeast.com/content/tools/RaidCalc/RaidCalc.asp

I thought 2 drives could make RAID 0+1? If assuming I need 4 disks and have 4 x 1TB, what would be the answer for my questions as above? I'm just worried of migrating the data at a later stage where it'll be lots of hassle.

[neonblingbling]

RAID 0+1 is like having 4 disks, 1 2 3 4. First imagine disks 1 and 2 are in RAID 0, with data A on disk 1 and data B on disk 2. Then, every thing is mirrored over to disks 3 and 4. So there is data A on disk 1 and 3, and data B on disk 2 and 4.

*It might actually be the other way around; I get RAID 0+1 and RAID 1+0 mixed up.

RAID 0:
A B
RAID 1:
A A
RAID 0+1:
A B A B

In any case, it's like having a RAID 0 setup with a mirrored image. To expand (from 4 disks to 6); you could keep one RAID 0 array (data A and B on disks 1 and 2). Then erase disks 3 and 4 and make a new RAID 0 array with disks 3, 4, and 5. Transfer data from the old array (disks 1 and 2) to the new array (disks 3,4,5). Then erase the old array, and make disks 1, 2, and 6 mirror the new array (disks 3, 4, 5).


Theoretically, RAID 0+1 of 4 disks should be the same speed as RAID 0 of 2 disks, but it might be a little slower because of more disks.

[SLORider]

Hey folks, I am running RAID-0 for some time and would like to explore the options for 0+1 but have some questions:

1. If I have 2 x 1TB disks running RAID0+1 and would like to add another 2 disks in future, do I need to re-format/re-configure the whole array?

2. Does RAID0+1 configuration of the above gives a better read/write speed compared to only RAID-0?

I'd like to partition my disk so that my C:\ would only have 100GB or so while the rest is in D:\ as it'll make my life easier every time I re-install my Vista :)

neonblingbling's description is correct. IF your RAID controller allows tearing down half your array then you could add drives as described.

RAID 0+1 is a mirror of striped sets: AB AB

Adding two more disks would simply add another mirror: AB AB AB

The two additional disks (the additional mirror) does not add additional storage. You must do what neonblingbling describes--tear down the mirror and rebuild each stripe set so that you end up with: ABC ABC

---

RAID 1+0 (RAID 10) is a stripe set of multiple mirrors: AA BB

RAID 10 is more fault tolerant than 0+1 because an entire mirror set has to fail before RAID 10 fails (both A's or both B's -- only TWO possibilities). With RAID 0+1, the odds of failure are higher as one failed drive in each stripe set causes failure (A+A, A+B, B+A, B+B -- there are FOUR possibilities). Also with RAID 10, all of the non-failed drives continue to work.

Adding another mirror to RAID 10 gives: AA BB CC

Your RAID controller must support extending the stripe set from across two mirrors to three--otherwise, you will have to back up before rebuilding.

---

Basically, it depends on your RAID controller. MORE IMPORTANT, you should never trust your data to survive tricky RAID reconfigurations anyway. Things never go as they are supposed to. You should always have a backup.

[aoch88]

Thanks everyone. I think I'll just go with RAID-0 and another normal disk to backup stuffs manually. I seriously don't want to ruin anything the next time I upgrade especially if we're talking about 1TB of data :(

[Endgame124]

RAID 0+1 is a mirror of striped sets: AB AB

Adding two more disks would simply add another mirror: AB AB AB

The two additional disks (the additional mirror) does not add additional storage. You must do what neonblingbling describes--tear down the mirror and rebuild each stripe set so that you end up with: ABC ABC

---

RAID 1+0 (RAID 10) is a stripe set of multiple mirrors: AA BB

RAID 10 is more fault tolerant than 0+1 because an entire mirror set has to fail before RAID 10 fails (both A's or both B's -- only TWO possibilities). With RAID 0+1, the odds of failure are higher as one failed drive in each stripe set causes failure (A+A, A+B, B+A, B+B -- there are FOUR possibilities). Also with RAID 10, all of the non-failed drives continue to work.


I actually thought it was the other way around, based on the numbering scheme. Raid 10 is a mirror (1) of Striped disks (0), where as Raid 0+1 is a stripe (0) of Mirrors (1).

Regardless of the actual numbering, assuming your controlly supports dual reads, (simultaneous, reads from each disk in a mirror) a mirror of striped disks should be slightly faster on reads than a 4 disk Raid 0 array.