Introduction to RAID : RAID Components and Features : Disk Rebuilds

Disk Rebuilds

When a drive in a RAID drive group fails, you can rebuild the drive by recreating the data that was stored on the drive before it failed. The Nytro MegaRAID controller recreates the data using the data stored on the other drives in the drive group. Rebuilding can be done only in drive groups with data redundancy, which includes RAID 1, 5, 6, 10, 50, and 60 drive groups.

The Nytro MegaRAID controller uses hot spares to rebuild failed drives automatically and transparently, at user-defined rebuild rates. If a hot spare is available, the rebuild can start automatically when a drive fails. If a hot spare is not available, the failed drive must be replaced with a new drive so that the data on the failed drive can be rebuilt.

The failed drive is removed from the virtual drive and marked ready awaiting removal when the rebuild to a hot spare begins. If the system goes down during a rebuild, the Nytro MegaRAID controller automatically resumes the rebuild after the system reboots.

*NOTE  When the rebuild to a hot spare begins, the failed drive is often removed from the virtual drive before management applications detect the failed drive. When the rebuild occurs, the events logs show the drive rebuilding to the hot spare without showing the failed drive. The formerly failed drive is marked as ready after a rebuild starts to a hot spare. If a source drive fails during a rebuild to a hot spare, the rebuild fails and the failed source drive is marked as offline. In addition, the rebuilding hot spare drive is changed back to a hot spare. After a rebuild fails because of a source drive failure, the dedicated hot spare is still dedicated and assigned to the correct drive group, and the global hot spare is still global.

An automatic drive rebuild does not start if you replace a drive during a RAID-level migration. The rebuild must be started manually after the expansion or migration procedure is complete. (RAID-level migration changes a virtual drive from one RAID level to another.)