[SATLUG] Understanding RAID and global hot spares

Daniel J. Givens daniel at rugmonster.org
Thu Dec 17 19:25:41 CST 2009

On 12/17/2009 4:56 PM, David Salisbury wrote:
> I've got a server-type box with an Intel RAID controller running SUSE
> Enterprise. One array with some 160g drives (3 in RAID 1 [2 plus a
> global hot spare]), and the 2nd array with some terabyte drives (3 in
> RAID 1 [2 plus a global hot spare]). Since I assigned each of those hot
> spares to the respective RAID array (the 160g hot spare to the 160
> array, the 1TB hot spare to the terabyte array), I was under the
> impression each hot spare would be used in each array, respectively.
> But, in testing this setup, I pulled a drive from the 160g array and it
> started using the terabyte hot spare to rebuild the array!! Not what I
> wanted to have happen. (I had already tested this once before, and it
> used the correct 160g hot spare. But this 2nd time it used the 1TB
> drive.) Am I not understanding the global hot spare? Do I need to
> configure the global hot spare to be "local" or something so that it
> doesn't hop arrays like that? If I DO have to do that, will
> reconfiguring the RAID array mess with or destroy the data on the drives
> I already have running?

By nature of "global" I would assume that it would use the next 
available hotspare, however it makes that determination, where ever. 
This is all going to be specific to your controller, but I would imagine 
you could remove the hotspares and re-add them as local hotspares. I 
can't imagine a controller of any value that would cause you to destroy 
the RAID volume to add/remove a hotspare.


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