What's the difference between RAID 0+1 vs 1+0?

[sun818]

I understand RAID 0 is striped and RAID 1 is mirrored. But I read some discussion referring to 0+1 and 1+0. Is there an advantage or disadvantage to running in either form?

 

[pallejr]

YES. pcguide explains it pretty well: http://www.pcguide.com/ref/hdd...f/raid/levels/mult.htm

 

[sun818]

thanks. I saw that too. I can visualize RAID 0+1 which is just a striped set being mirrored. Minimum of 4 disks. Disk 1 & 2 can be striped. Disk 3 & 4 would be mirror of Disk 1 & 2.

But I can't visualize RAID 1+0 for some reason.

 

[Madwand1]

This section focuses on the differences:

http://www.pcguide.com/ref/hdd...d/levels/multXY-c.html

However, some vendors confuse the issue further by describing their implementations as RAID 10 when it actually behaves as RAID 0+1 described above.

 

[xitshsif]

The thing to realize with RAID is that an array appears to the outside as a single disk. The fact that it's made of 2 mirrored disks or 2 striped disks is irrelevant. RAID 1+0 is where you have two mirrored pairs, 1+2 and 3+4. Each of these appears as a single disk, A and B. The RAID 0 is just striping across disks A+B. The RAID controller doesn't care that A and B are actually made up of multiple physical disks. This way either of the disks in A or B could fail and the striped array would still function.

No idea if that clears things up at all. I guess the biggest point is that each RAID array acts like a disk; you can RAID arrays just like you can RAID disks.

 

[sun818]

thanks xitshsif - that helps. Initially, I wasn't grasping that you can stripe multiple physical disks that logically appear as a single drive. It sounds like other than paying more upfront for the cost of a controller, RAID 1+0 looks to be the better configuration over RAID 0+1.

 

[xitshsif]

As far as I know, controllers that do RAID 0+1 generally also do 1+0. Personally I think a better use for 4 disks would be RAID 5. Note that I've never actually used RAID, but I've done my share of reading.

 

[sun818]

Here's a diagram of RAID 1+0:
http://en.wikipedia.org/wiki/Nested_RAID_levels#RAID_10

For storage utilization RAID 5 is better than mirroring. But I'm looking to boost my write performance on my workstation. From what I'm reading, RAID 1+0 should do a better job than RAID 5. SATA drives in the 150-250GB range are so cheap now, I don't mind sacrificing 50% of my storage for RAID 1+0.

 

[xitshsif]

Okay, if you're looking for write performance, 1+0 would be the way to go. The average user looking to RAID here usually is doing it for storage and media streaming, which RAID 5 would make the most sense for - backup with high storage efficiency.