If a disk is temporarily disconnected from its RAID group and then reconnected, the RAID group must resynchronize all of its data. This process may take a long time. If the RAID group has a bitmap, only changes that were made after the disk was removed need to be synchronized, greatly speeding up the process.
A disk can become temporarily disconnected in the following situations.
A disk is accidentally removed from the NAS while the NAS is powered on.
The NAS unexpectedly shuts down because of a hardware or software error.
A user presses the power button for 10 seconds or disconnects the power cable while the NAS is powered on.
You can only create bitmaps for RAID 1, RAID 5, RAID 6, and RAID 10 groups.
Enabling a RAID bitmap causes the RAID groups performance to decrease slightly.
A bitmap improves resynchronization time only if the same disk is added back to the RAID group. If a new disk is added to a RAID group, the bitmap makes no difference.
A confirmation message appears.
QTS creates a bitmap for the RAID group.