RAID Bitmaps
If a disk is temporarily disconnected from its RAID group and then reconnected, the RAID group must synchronize all of its data. This process may take a long time. If the RAID group has a bitmap then only changes that were made after the disk was disconnected need to be synchronized, greatly speeding up the process.
A disk can become temporarily disconnected in the following situations.
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A disk is accidentally removed from the NAS while the NAS is powered on.
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The NAS unexpectedly shuts down because of a hardware or software error.
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A user presses the power button for 10 seconds or disconnects the power cable while the NAS is powered on.
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You can only create bitmaps for RAID 1, RAID 5, RAID 6, and RAID 10 groups.
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Enabling a RAID bitmap may slightly decrease the read and write performance of the RAID group.
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A bitmap improves synchronization time only if the same disk is disconnected then reconnected. Having a bitmap does not improve synchronization time when a new disk is added to the RAID group.
Creating a RAID Bitmap
QTS creates a bitmap for the RAID group.