• When RAID6 with ADG is used, two drives can fail simultaneously (and be replaced simultan-
eously) without data loss.
• If the offline drive is a spare, the degraded drive can be replaced.
Do not remove a second drive from an array until the first failed or missing drive has been replaced
and the rebuild process is complete. (The rebuild is complete when the Online LED on the front of
the drive stops blinking.)
• In RAID6 with ADG configurations, any two drives in the array can be replaced simultaneously.
• In RAID1+0 configurations, any drives that are not mirrored to other removed or failed drives
can be simultaneously replaced offline without data loss.
Automatic data recovery (rebuild)
When you replace a disk drive in an array, the controller uses the fault-tolerance information on the
remaining drives in the array to reconstruct the missing data (the data that was originally on the
replaced drive) and write it to the replacement drive. This process is called automatic data recovery,
or rebuild. If fault tolerance is compromised, this data cannot be reconstructed and is likely to be
Time required for a rebuild
The time required for a rebuild varies considerably, depending on several factors:
The priority that the rebuild is given over normal I/O operations (you can change the priority setting
by using ACU)
The amount of I/O activity during the rebuild operation
The rotational speed of the disk drives
The availability of drive cache
The model and age of the drives
The amount of unused capacity on the drives
The number of drives in the array (for RAID5 and RAID6 with ADG)
Allow approximately 5 minutes per gigabyte without any I/O activity during the rebuild process. This
figure is conservative, and newer drive models usually require less time to rebuild.
System performance is affected during the rebuild, and the system is unprotected against further drive
failure until the rebuild has finished. Therefore, replace drives during periods of low activity when
If the Online LED of the replacement drive stops blinking and the amber fault LED glows, or if other
drive LEDs in the array go out, the replacement drive has failed and is producing unrecoverable disk
errors. Remove and replace the failed replacement drive.
When automatic data recovery has finished, the online LED of the replacement drive stops blinking
and begins to glow steadily.
Failure of another drive during rebuild
If a non-correctable read error occurs on another physical drive in the array during the rebuild process,
the Online LED of the replacement drive stops blinking and the rebuild abnormally terminates. If this
D2600/D2700 Disk Enclosure User Guide