Smart Array 6402/128 RAID 10 2 disks ??

[Avgoustakis]

Hi all,

Our HP specialists told me that the Smart Array 6402/128 allows RAID 10 with only 2 disks ? Is this true or is this not really a RAID 10 configuratio ? If possible are there any limitations ?

I always thought that RAID 10 needed at least 4 disks ?

Thanks for the feedback !

Stefan

[JohnWRuffo · Accepted solution]

Stefan:

HP references RAID 1 and RAID 1+0 as the same config in the ACU.

To build a true RAID 1+0 you need at least 4 disks.

Hope this helps! -john

[Avgoustakis]

John,

Thanks for the info.

They should change it don't you think ?? The info is quit misleading.

Anyway I'm happy you could clear my doubts.

Greetz,

Stefan

[JohnWRuffo]

Yes... I think a clairification could be made, but if you read their definition:

"
Fault Tolerance Keeps data available and server running while a failed drive is being replaced; several fault tolerance configurations are supported including:

Drive Mirroring (RAID 1, 1+0): This allocates half of the drive array to data and the other half to mirrored data, providing two copies of every file. It is a high-performance RAID configuration.
"

it is essentially correct. The rest of use just see the configuration requirements first and the order last.

http://h18004.www1.hp.com/products/quickspecs/11587_na/11587_na.html#Product%20Highlights

[Avgoustakis]

John,

Does this mean that:

A)If I use 4 disks, and choose the RAID 1+0 option in the controler menu, that it wil automatically create 2 mirrored arrays and then stripe them without any xtra config?

B) If I use 2 disks, and choose the RAID 1+0 option in the controler menu, it will just mirror the 2 disks ?

Txs for the feedback.

[Steven Clementi]

I think a better way to look at this is that....

The array is your "striped" (RAID0) part and when you define the logical drive RAID 1 or RAID 1+0, the logical is actually RAID1. Hw does the Smart Array handle it?.....

for a 2 drive array, it is easy. All files are striped across the drives. eg. file 1 is on drive 1, file 2 is on drive 2, file 3 is on drive 1, etc.

Then for RAID1, the stripe is mirrored. File 1 is mirrored on drive 2, file 2 on drive 1, file 3 on drive 2, etc.

The SA obviously works at a block level, not a file level, but I think the same holds true. This gives you the redundancy of RAID 1 and the performance of multiple drives in an array.

For an array with 4 drives? Same theory. file 1 on drive 1, f2 on d2, f3 on d3 and f4 on d4. Then the mirroring, m1 on d2, m2 on d3, m3 on d4 and m4 on d1. Now, there might be some mix up of the order, but as long as the file is mirrored on a different drive, then RAID1+0 comes into play.

In older times, like on the HSG80, RAID 1+0 was where you needed to have at least 4 drives since you would create your mirror sets first, then sripe your mirror sets and creat your units from the stripes.

On a standard SA or MSA, you can't manually create true RAID 1+0 since you can not create an array with no logical drives nor can you create an array from an array.


Steven

[libor4u]

Hi Steven,

from your description it looks more like 0+1, not 1+0. Am I correct?