Dell PowerVault MD3820f - Manual (Page 221)

data from peer disks in the disk group and uses recovered data to correct the error. If the controller
encounters an error while accessing a peer disk, it is unable to recover the data and affected sectors are
added to the unreadable sector log maintained by the controller. Other conditions under which sectors
are added to the unreadable sector log include:
• A media error is encountered when trying to access a physical disk that is a member of a
nonredundant disk group (RAID 0 or degraded RAID 1, RAID 5 or RAID 10).
• An error is encountered on source disks during rebuild.
NOTE: Data on an unreadable sector is no longer accessible.
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