global hot spare drive


Dell is building new domain controller for me. I'd like have global host spare drive in this server.


Server power edge r620
RAID 1 (OS) - 2x 600 GB
RAID 5 (DATA) 4 x 600 GB

What single drive I should use as global hot spare (what size) and how should be configured (where connected, any raid should be on it ?)

I have pretty hard time to get correct answer from DELL.
thank you,

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PowerEdgeTechIT ConsultantCommented:
It should not be a hard question for the sales guys at Dell to answer.

In order for a disk to be a hot-spare, it must be AT LEAST as large AND the same type (SAS/SATA) as the disks in the array(s) it will protect.

Both of your RAID arrays use 600GB SAS disks, so your hot-spare must be a 600GB SAS disk.  It can be larger, but I'm not sure why you would get a larger one - there is no advantage.

To utilize a hot-spare, you simply assign that role to a disk that is not currently being used in an array:

Global HS:  Will protect both of your arrays.  If a disk fails from either array, the HS will rebuild in its place.

Dedicated HS:  Will protect ONE array - whichever array you assign the hot-spare to.  If you assign the HS as dedicated to the RAID 1, and a disk fails from the RAID 5, then the HS will NOT rebuild in the failed disk's place - ONLY if a RAID 1 disk fails.

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The global hot spare needs to be >= the capacity of the largest disk drive you have in an array with the same technology. If largest SAS disk you have is 1TB then it needs to be >= 1TB.

If you mix & match SAS & SATA then you will need a SAS hot spare and a SATA hot spare.
Hi Henryk123,

Per your current config.  Your primary boot drive containing your OS is Raid 1 meaning they are mirrored.  So, every time something is written to disk 1 the same is written to disk 2. Fast and contains mirror backup.

Your Data volume is Raid 5 which in this case is not really the best situation only having 4 drives.  The minimum drives for Raid 5 is 3 and you can have a hot spare with it or no hot spare at all.  So, if none of these drives are hot spares and a drive fails you stay up but loose a 2nd drive you  will loose all the data.

That is why I would have used all drives in a Raid 5 array with one drive as a hot spare.  Remember with Raid 5 its N-1 with one drive being used for parity.
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