P400 Raid5 disk increase

[agent006]

We have a DL380 G5 with 4x 72GB SAS in RAID5. We need to add more storage, so are planning on adding an extra two 146GB SAS. Is it possible to add these extra disks to the same RAID volume, and just increase the volume size? I've done this before with same sized disks, but not with larger. I'm concerned that the array won't use the full size of the extra disks.

Am I right to be concerned about this, or will it just work?

[TTr · Accepted solution]

If you add 146GB disks to the existing raid5 array, only 72GB (half) of the disk) will be used. The remaining half space will *not* be accessible in any way.

[gregersenj]

"The remaining half space will *not* be accessible in any way"
That is not entirely true TTr
It can be used for a one disk RAID 0.

BR
/jag

[cnb]

"That is not entirely true TTr
It can be used for a one disk RAID 0."

@gregersenj: WOW. Um...NO. YOU need to re-read the posted question and the RAID 5 specs:

http://en.wikipedia.org/wiki/RAID_5#RAID_5

"Therefore, the usable capacity of a RAID 5 array is (N-1) * Smin, where N is the total number of drives in the array and Smin is the capacity of the smallest drive in the array."


He's wants to add 146GB disks to the EXISTING RAID 5 volume and yes TTr is correct, the expanded R5 array volume will only use ~72GB on each new disk.

Mixing disk sizes in a RAID 5 is not recomended because it will use only the smallest size and the remaining space in that VOLUME will be unusable.

Agent006: TTr is correct, you will lose the space. Best to migrate to all 146GB disks or larger for your RAID5 volume.

Rgds,

[gregersenj]

What I meant is.

You will be left over with some unused space, on the new large disk.

On that space you can create a new logical drive.

But you are right I should re-read the post. agent006 want to add 2 disks.

So if 2 disks of 146 Gb is added to the array. the RAID 5 can be expanded and extened with 2 x72 GB.
This will leave 2 x 74 GB of unused space on the 2 new drives.
That can be used for a RAID 1 of 74 GB or a RAID 0 of 148GB

[cnb]

@gergensenj:
>"What I meant is.

You will be left over with some unused space, on the new large disk.

On that space you can create a new logical drive."

NO you can't. You don't know what you are talking about. If you think you can, then obviously you don't understand the R5 spec.

RTFM.

If you still think you can, try it yourself before telling people they can, and then please post your findings with screen shots and metadata configuration listings.

4 x 72 GB disks in a R5 volume add 2 more 146GB disks to that volume gives you 6 x 72GB of R5 space and you cannot allocate the "unused" R5 space another RAID volume of any sort BECAUSE THERE ISN'T ANY UNUSED SPACE.


WHAT PART OF "In RAID 5, the yield is Smin * (n-1), where Smin is the size of the smallest disk in the array." DON'T YOU UNDERSTAND???

http://en.wikipedia.org/wiki/RAID_5#RAID_5

Read, re-read and then read it again until you understand the R5 formula.


Rgds,

[gregersenj]

This is a Smart Array controller.

Using the ACU it is posible to create multible logical drives, within the same Array.

Simply:
add new drives
using ACU, expand array
using ACU, extend excisting logical drive.
using ACU, create new logical drive on the unused space.

having two disks with unused space, give you the availability to create a RAID 0 or RAID 1

Note: There's a down side, having multible logical drives on an array.
The smart array controller can extend the upper logical drive only.
So if you choose to use this ampty space, and you have to add more disks in the future, you most likly have to delete the upper logical drive, to extend the lower.

note:
On the smart array controller. Creating an array, define wich physical disks, is in the same work groupe. It does not define the RAID level here.
The RAID level and size is defined when you create the logical drives.
So you can create multible RAID's of different RAID levels, on the same physical disks.
It's all in the ACU user guide.

HP took advanged of these features, on some of the All in One solutions.
The put 4 physical disks in the server.
Created two equal size RAID 1's.
Mirror 1 on disk 1 and 2.
Mirror 2 on disk 3 and 4.
The only used a minor part of the disks for the mirror's.
And then created a RAID 5 on the remainig space.

BR
/jag