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Software RAID-5 in SoftRAID
RAID-5 is a fault-tolerant storage approach which allows the failure of one drive.
For software RAID-5, SoftRAID 5 is the first and only choice for Apple OS X as of mid 2014. It offers high performance (better than most hardware RAID), and an easy to use feature set.
This page shows various aspects of using RAID-5 in SoftRAID.
5-drive RAID-5
A 5-drive RAID-5 in SoftRAID. All drives are operating normally, so full fault-tolerance in in effect—one drive can fail and the RAID continues to operate.

Adding a replacement drive
A drive has failed. Replace the drive so that the rebuild process can begin.
Having a cold spare on hand lets the rebuild process start immediately, so that fault tolerance can be restored. Not having a spare means that the rebuild process is delayed, which puts the RAID-5 at risk of a 2nd drive failure, which would be fatal to the volume.

4-drive RAID-5 , degraded but rebuilding
One of the drives has failed and has been replaced.
SoftRAID is rebuilding the RAID-5 to restore fault-tolerance.

When the RAID-5 has been rebuilt, SoftRAID posts a notification.
