Raid 1/0 and raid 0/1

[aliasgar]

Hi,
Can anyone clearly give the concepts of Raid level 1/0 and 0/1 as some of the documents are confussing.


Thanks and Regards,

[Robert_Jewell]

Well, I can give you some basics:

RAID 0 is striping
RAID 1 is mirroring

RAID 0/1 would be a striped set that has been mirrored.

Disk A, B and C are striped, creating RAID 0.
Disk D, E and F are also striped, creating another RAID 0.

Now boths sets of striped drives are mirrored.

RAID 1/0 would be multiple mirrors striped together.

Disk A and B are mirrored.
Disk C and D are mirrored.
Disk E and F are mirrored.

All three of these are now striped together.

Hope that offered a basic explanation, but I am sure that there are more detailed answers out there if you need them.

-Bob

[Insu Kim]

RAID 1/0 is the same as RAID 0/1.

RAID 0 indicates striping and data is striped across all disks in the LUN.
The ability to access all disks in the LUN simultaneously provides a high I/O rate.
RAID 0 diesn't provide any data redundancy.

RAID 1 uses hardware mirroring to achieve data redundancy and provides good performance, but at the cost of storage efficiency. Because all data is mirrored, a RAID 1 LUN has a storage efficiency of 50%.

RAID 1/0 uses mirroring to achieve data redundancy and disk striping to enhance performance. It combines the speed advantage of block striping with the redundancy advantage of mirroring.
Because all data is mirrored, a RAID 1/0 LUN has a storage efficiency of 50%.

A RAID 1/0 LUN contains an even number of from 4 to 30 disks.
One half of the disks are primary disks and the other half are disk mirrors.
When a disk fails, the array uses the remaining disk of the mirrored pair for data access.

Hope this helps,

[aliasgar]

Hi,

Thanks for answering,but Robert can u give more clear picture of Raid 1/0 where u mentioned the last line that

Disk A and B are mirrored.
Disk C and D are mirrored.
Disk E and F are mirrored.

All three of these are now striped together.

Thanks,

[aliasgar]

Hi,

Thanks for answering,but Robert can u give more clear picture of Raid 1/0 where u mentioned the last line that

Disk A and B are mirrored.
Disk C and D are mirrored.
Disk E and F are mirrored.

All three of these are now striped together.

Thanks,

[Enes Dizdarevic]

There is a difference between raid 1/0 and raid 0/1 in the way how disks are accessed. As Robert explained in raid 1/0 you have multiple raid1 stripped. First block of data is writen on disk A and its mirror disk B. Next block is also writen od disk A and its mirror. When all available data on the first mirror set (disks A and B) are used raid 1/0 starts using second mirror set. In some documents this is called raid 10 and this is usually implemented in low end disk controllers as NetRaid for netservers for example.
In Raid 0/1 you have raid 0 mirrored with another raid 0 (in Robert's example, raid 0 created from disks A, B and C is mirrored with raid 0 created from disks D, E and F). That means that data which should be writen are divided into 3 block and first block is written on disk A, second on disk B, etc. This data is also writen on mirrored raid0.
From the capacity point of view there is no difference between raid 1/0 and 0/1 but there is a difference from the performance point of view. In raid 1/0 data is written to only one disk (and its mirror), in raid 0/1 data is spread to all disks in first raid0 (and its mirror) and you have better performance due to the fact that data is written to multiple disks simultanously. Raid 0/1 is usually implemented in midle range and high end disk arrays, VA and XP for example.

[Volker Borowski]

In addition to what Enes explaines on Performance, there is a diffrence in safety:

Having Disk A+B+C Striped and mirrored to Stripeset D+E+F, a loss of disk A and E will damage your entire stripeset while a stripeset build upon the mirrored disks A+D/B+E/C+F will remain intact and only be destroyed, if the corresponding mirror disks go bad at once.

Volker

[Insu Kim]

Thank you for making me to know this subtle difference between RAID 0/1 and RAID 1/0.
I thought that they're the same but that was my misunderstanding.
Thanks again for submitting this matter in the forums.
In addition to the concept of RAID 0 and RAID 1, see below.

Let's look at RAID 0+1 first.
This combination uses RAID 0 for it's high performance and RAID 1 for it's high fault tolerance. I actually mentioned this level when I talked about adding striping to mirroring. Let's say you have 8 hard drives. You can split them into 2 arrays of 4 drives each, and apply RAID 0 to each array. Now you have 2 striped arrays. Then you would apply RAID 1 to the 2 striped arrays and have one array mirrored on the other. If a hard drive in one striped array fails, the entire array is lost. The other striped array is left, but contains no fault tolerance if any of the drives in it fail.

RAID 1+0 applies RAID 1 first then RAID 0 to the drives. To apply RAID 1, you split the 8 drives into 4 sets of 2 drives each. Now each set is mirrored and has duplicate information. To apply RAID 0, you then stripe across the 4 sets. In essence, you have a striped array across a number of mirrored sets. This combination has better fault tolerance than RAID 0+1. As long as one drive in a mirrored set is active, the array can still function. So theoretically you can have up to half the drives fail before you lose everything, as opposed to only two drives in RAID 0+1.

Hope this helps,

[Robert_Jewell]

I hope the above reply's above clarify what you were looking for. And didnt I tell you there would be plenty more answers :)

[Brian M Rawlings]

Sorry to respond to such an old thread, but I came across a web site that illustrates this (graphically), and has a fairly decent discussion of the issues. I decided to reply so that any who find this thread in their research can check it out:

http://www.ofb.net/~jheiss/raid10/

Regards, --bmr