The DDP typically uses RAID 5 and RAID 6 levels as it provides a protection against read errors, as well as whole disks failure. With RAID 5, one drive breakdown is tolerated. With RAID 6 up to two drives failures can be tolerated without any data loss.

For an extra security, the DDP can also be configured with hot spare drives so that the RAID arrays can be automatically rebuilt in case of drive failure.

This can be done by logging into the Areca web interface, and then going to the “Create hot spare” entry under the “RAID Set Functions”.
A full list of the free drives that can be used as hotspares is displayed.

If no free disk is available for it means all the drives are either already part of RAID set, either already assigned as hotspare.
In that case it means you need to change the RAID set structure in order to release at least one drive.
The drives assignment can be seen in the “RAID Set Hierarchy” under the “Information” menu.

When there is at least one hotspare drive configured, it will be used whenever one other drive fails and the data will start rebuilding.
Of course after you replace the failed drive by a new one, you still need to reassign that new drive as a hotspare so that it can be used in case of further troubles.

After replacing the failed drive, it might happen that the new drive doesn’t appear in the list of free drive.
Two situations can explain that problem:

- The drive is not actually new and has been previously marked as failed by the Areca card.
In that case you can activate it by going to the “Activate Failed Disk” entry of the “Physical Drives” menu.
Then select the drive and activate it so that you can see it under the “Create Hot Spare” page list and assign it as a hotspare.

When that is not possible for some reason, please refer to the procedure below.

- No matter what drive is inserted, it will be displayed as a failed drive. This is known issue that can happen for a given slot after one drive has failed as shown in the screenshot below:

To solve the situation, you just need to reboot the DDP, after which the new drive will be considered as free and listed as a usable hotspare.