Replacing hard drives in a NetApp aggregate

NetApp uses certain rules to assign hot spares in case of a failure. It always tries to use the exact match, but if it’s not there, the best available spare is used. “The best” means that if you have an aggregate which consists of 1TB hard drives and you have only 2TB spare left, then this 2TB spare will be downsized to 1TB and used as a data disk. After that, when you receive a correct size replacement from NetApp, you need to exchange the downsized 2TB hard drive with the delivered 1TB spare. To accomplish that, use the following command:

> disk replace start disk_name spare_disk_name

It will take considerable amount of time to copy the data. In my case it was 6.5 hours for a 1TB drive.

When the process finishes, replaced drive becomes a new spare. It’s wise to zero it out right away, so that it could be easily used again as a spare. Otherwise when time comes you’ll be waiting hours before it could be added in place of the failed drive:

> disk zero spares

As a side note I want to mention that you cannot take disks out of the raid group. There is no way to shrink aggregates. The only thing you can make is to replace a hard drive with another one.

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IBM DS4700 copyback failed

If you have a global hot spare (GHS) drive when one of the active hard drives failes, your data is reconstructed to a GHS. Then, when you replace the failed drive, storage system automatically initiates a copyback, which gets the data from the GHS back to the replacement drive. Sometimes it doesn’t happen and replacement drive stays in an Unassigned state. If it is the case go to the DS Storage Manager, right click on the RAID array and select Replace Drives. There you should see the failed drive. Choose replacement from unassigned drives and click Replace Drive. Copyback will start immediately.

Take into consideration that copyback can be long-lasting, depending on the array size. If it is a production system and its performance is critical, right click on the logical drive, choose Change -> Modification Priority. There you can set how much resources will be allocated for modification (such as copyback, reconstruction, etc) and performance. Change it to Low for maximum performance.