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Configuring a hot spare
I have a two enclosures:
Enclosure 0:
Disks 0-14 (146GB)
Enclosure 1:
Disks 0-9 (146GB)
Disks 10-14 (300GB)...Just added.
Before the new disks were added I had a hot spare configured on Enclosure 0 Disk 14. I create a new RAID group and then two LUN's with the new drives. I also created another hot spare on Enclosure 1 Disk 14.
My question is how to make the new RAID 5 group failover to the newly created hot spare?
Dev Mgr
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July 25th, 2009 08:00
With EMC systems, all hotspares are global and they automatically fail back. This means that any hotspare will take over for any failed drive, and once the original drive is replaced (and the hotspare has finished rebuilding), the hotspare mirrors back to the replacement drive, after which the hotspare becomes a hotspare again.
However, there is a logic to how a hotspare is picked.
If memory serves me right, the steps are:
- look for a hotspare on the current bus first
- look for the first hotspare you can find (starting in enclosure 0, then 1, and up from there)
- verify the hotspare has enough space to rebuild all luns in the raid group of the failed drive (note: a 146GB (~133GB usable) hotspare can fail over for a 300GB drive if the 300GB drive doesn't have more than ~133GB of actual data/luns)
3 example scenarios:
- you have a 146 fail, it'll use your 146 hotspare. If a 2nd 146 fails (before your first failure is replaced and the hotspare finished mirroring back) it'll use the 300.
- you have a 146 fail, the 146 hotspare kicks in. Now a 300 fails, the 300 hotspare kicks in.
- you have a 300 fail, your 146 hotspare isn't large enough, so it skips this and picks the 300GB hotspare. If a 146 were to fail, your 146 hotspare picks up.