APC iSCSI SATA II - Manual (Page 71)

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Chapter 4 Advanced Operation
4.1 Rebuild
If one physical disk of a Raid Group, which is set to a protected RAID level (e.g.: RAID
3 , RAID 5, or RAID 6), is FAILED or has been unplugged/removed, the RG status is
changed to degraded mode. The system will search/detect spare disk to rebuild the
degraded RG to a complete one. It will try to detect dedicated spare disk first, then
global spare disk, to rebuild.
The iSCSI RAID subsystem supports Auto-Rebuild function. The following is the
scenario:
Take RAID 6 for example:
1. When there is no global spare disk or dedicated spare disk on the system, the
subsystem will be in degraded mode and wait until (A) there is one disk assigned
as spare disk, or (B) the failed disk is removed and replaced with new clean disk,
then the Auto-Rebuild starts. The new disk will be a spare disk to the original RG
automatically.
a. If the new added disk is not clean (with other RG information), it would be
marked as RS (reserved) and the system will not start "auto-rebuild".
b. If this disk is not belonging to any existing RG, it would be FR (Free) disk
and the system will start Auto-Rebuild function.
c. If user only removes the failed disk and plugs the same failed disk in the
same slot again, the auto-rebuild will start by this case. But rebuilding in
the same failed disk may impact customer data later if the disk status is
unstable. It is not recommended to rebuild on the same failed disk for
better data protection.
2. When there is enough global spare disk(s) or dedicated spare disk(s) for the
degraded array, the subsystem starts Auto-Rebuild immediately. And in RAID 6, if
there is another disk failure happening during the time of rebuilding, the
subsystem will start the above Auto-Rebuild scenario as well. Auto-Rebuild feature
only works when the status of RG is "Online". It will not work at “Offline” status.
Thus, it will not conflict with the “Roaming” function.
3. In degraded mode, the status of RG is “Degraded”. When rebuilding, the status
of RG/VD will be “Rebuild”, the column “R%” in VD will display the ratio in
percentage. After complete rebuilding, the status will become “Online”. RG will
become complete.
NOTE: “Set dedicated spare” is not available if there is no RG or
RAID level is 0 or JBOD, because dedicated spare disk can not be
set to RAID 0 & JBOD.