What happens when I validate a mirror volume?

SoftRAID validates a mirror volume by reading every sector from each of the disks in the volume, and comparing them to ensure they all have the correct data—ie the mirrored data is identical to the data it’s mirroring. If a mismatch is found, SoftRAID will update all blocks on the volume’s disks with the correct data. The SoftRAID application displays a count of the number of blocks updated whenever you validate a mirror volume. Since each disk can be used for more than one volume, only the parts of the disk that contain the actual volume being validated are checked.

If a mirror volume has been validated successfully with SoftRAID, you are guaranteed that all the disks for that mirror volume contain identical data.

You can read more about the validation process and how it works for other volume types here.