IBM N-Series (NetApp) default disk sparing

Had an issue recently with a customers new N3300 NAS and the amount of hot spare disks OnTAP wants to keep. This particular customer ordered a clustered model (A20), along with an EXN4000 disk shelf containing 14 x 300GB disks.

When we fired it up, the controllers had taken ownership of all the disks evenly (7 per controller), set each of its vol0 to a 266GB usable RAID-DP configuration (3 disks gone) and with two hot spares each. Now from the original 14 physical disks, we were now down to 4 disks left out of 14 to work with! No problem, lets jump into FilerView and add one of the hot spares into aggr0 to get some more space… no bingo… “The number of spare disks remaining is too little for the requested parity”…

It seems this hot sparing change to OnTAP only came in recently (we’re running version 7.2.4L1), and I must say it seems a little crazy to force 2 hot spares for each controller set in such a small configuration, the crazier part was how difficult it was to find out how to reduce the hot spare count.

After trying many different command combinations sent to us by IBM & NetApp we finally found one which did the trick, and allowed us to drop the hot sparing back to a single disk per controller…

This command needs to be entered in the CLI to reduce the minimum amount of hot spares required…

options raid.min_spare_count <number of spares>

All good?  Sort of – The FilerView still does not allow you to expand the aggregrate any further, it still kept reporting “The number of spare disks remaining is too little for the requested parity” error when you try to add in an additional disk to aggr0. Jumping back into the CLI however, would let us add another disk into aggr0, expanding our usable space by 300GB per controller. The command for doing this;

aggr add aggr0 1@300
*300 being the size of my disk available

Has anyone else encountered this?  I must admit I’m still very new to these devices, so this may be common knowledge to many more experienced NetApp pilots out there.