Areca 24/4 Internal/External Port Pcie 3.0 12 Gb/s SAS/SATA Raid Controller 2Gb Cache - Manual (Page 251)

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APPENDIX
In the normal status, the newly installed drive will be recon-
figured an online free disk. But, the newly-installed drive is
automatically assigned as a hot spare if any hot spare disk
was used to rebuild and without new installed drive replaced
it. In this condition, the Auto Declare Hot-Spare status will
be disappeared if the RAID subsystem has since powered off/
on.
The Hot-Swap function can be used to rebuild disk drives in
arrays with data redundancy such as RAID level 1, 1E, 3, 5,
6, 10, 30, 50 and 60.
• Auto Rebuilding
If a hot spare is available, the rebuild starts automatically
when a drive fails. The RAID controllers automatically and
transparently rebuild failed drives in the background at user-
definable rebuild rates.
If a hot spare is not available, the failed disk drive must be
replaced with a new disk drive so that the data on the failed
drive can be automatically rebuilt and so that fault tolerance
can be maintained.
RAID controllers will automatically restart the system and
rebuilding process if the system is shut down or powered off
abnormally during a reconstruction procedure condition.
When a disk is hot swapped, although the system is function-
ally operational, the system may no longer be fault tolerant.
Fault tolerance will be lost until the removed drive is replaced
and the rebuild operation is completed.
During the automatic rebuild process, system activity will
continue as normal, however, the system performance and
fault tolerance will be affected.
• Adjustable Rebuild Priority
Rebuilding a degraded volume incurs a load on the RAID sub
system. The RAID controllers allow the user to select the