What is the difference between RAID 0+1 and 1+0?

[kunderian]

Is one faster or more reliable than the other?

 

[DaveSimmons]

Read the RAID FAQ on the main AT site. 0=striping (for speed) 1=mirroring (for reliability).

If you want to know "is RAID worth it?" then search "RAID" in this forum, both current threads and archives, for a few dozen earlier deabtes on this topic.

 

[Lord Evermore]

Unsurprisingly, the FAQ doesn't actually answer the exact question.

Pretty sure that 0+1 and 1+0 means the same thing, a striped mirror set, just a preference for the numbering. RAID 10 is another name for the same thing.

 

[Sunner]

Shoulds pretty much explain itself if you just think about it.

"Striped mirrors" versus "Mirrored stripes"

If you have two stripes(0) with three disks each, and one disk fails in each stripe, it's all gone.
If you have three mirrors with two disks each, in one stripe, then one disk per mirror can fail before the whole is gone.

 

[Sunner]

Originally posted by: Lord Evermore
Unsurprisingly, the FAQ doesn't actually answer the exact question.

Pretty sure that 0+1 and 1+0 means the same thing, a striped mirror set, just a preference for the numbering. RAID 10 is another name for the same thing.

No, it can be done both ways, though one clearly has a major advantage in terms of reliability.

 

[LeeTJ]

Originally posted by: Sunner
Shoulds pretty much explain itself if you just think about it.

"Striped mirrors" versus "Mirrored stripes"

If you have two stripes(0) with three disks each, and one disk fails in each stripe, it's all gone.
If you have three mirrors with two disks each, in one stripe, then one disk per mirror can fail before the whole is gone.

striped mirrored would required 4 disks, 2 striped mirrored on 2 striped.


seems to me would have the same security performance but striped mirrored would use fewer disks.

 

[Sunner]

Originally posted by: LeeTJ

Originally posted by: Sunner
Shoulds pretty much explain itself if you just think about it.

"Striped mirrors" versus "Mirrored stripes"

If you have two stripes(0) with three disks each, and one disk fails in each stripe, it's all gone.
If you have three mirrors with two disks each, in one stripe, then one disk per mirror can fail before the whole is gone.

striped mirrored would required 4 disks, 2 striped mirrored on 2 striped.


seems to me would have the same security performance but striped mirrored would use fewer disks.

I used the 2x3(mirrored stripes) and 3x2(striped mirrors) example to illustrate the redundancy difference between the two.
You can use many more disks if you feel like it, the more you use, the more obvious the advantage of striped mirrors vs mirrored stripes will become.

 

[Pariah]

Originally posted by: LeeTJ

Originally posted by: Sunner
Shoulds pretty much explain itself if you just think about it.

"Striped mirrors" versus "Mirrored stripes"

If you have two stripes(0) with three disks each, and one disk fails in each stripe, it's all gone.
If you have three mirrors with two disks each, in one stripe, then one disk per mirror can fail before the whole is gone.

striped mirrored would required 4 disks, 2 striped mirrored on 2 striped.


seems to me would have the same security performance but striped mirrored would use fewer disks.

Both require at least 4 drives. 2 for the RAID 1 part and 2 for the RAID 0 part. Technically you can have as many drives as you want in either RAID array provided the controller supports it and you have an even number of drives (you can't have an odd number of drives when mirroring is involved).

It's easiest to compare the 2 arrays when using only 4 drives.

With RAID 0+1 you have a mirrored array whose segments are RAID 0 arrays. In simple terms you have a RAID 0 array which is mirrored with the same RAID 0 array. Since you basically have 2 RAID 0 arrays no matter how many drives are in the array, only one lost drive will cost you any redundancy the array had since one RAID 0 array is gone leaving you with only a RAID 0 array. If you lose another drive, which would be in the remaining RAID 0 array, all your data would be lost.

With RAID 10 (1+0) you have a striped array whose segments are RAID 1 arrays. In simple terms you have 2 RAID 1 arrays, which are striped in a RAID 0 array. This configuration has potentially much better fault tolerance because if you lose one drive, all the remaining drives are still mirrored, meaning you can potentially lose half your drives and the array will still have its data. Of course, you can still lose your data with 2 dead drives if both drives are in the same mirrored pair.