Chapter 4 Advanced Operation; Rebuild - Sans Digital iSCSI STORAGE User Manual

Chapter 4 Advanced operation

4.1

Rebuild

If one physical disk of the RG which is set as protected RAID level (e.g.: RAID 3, RAID 5, or RAID 6) is
FAILED or has been unplugged/removed, then the status of RG is changed to degraded mode, the system
will search/detect spare disk to rebuild the degraded RG to a complete one. It will detect dedicated spare
disk as rebuild disk first, then global spare disk.
EliteRAID and TowerRAID iSCSI Seriess support Auto-Rebuild. The following is the scenario:
Take RAID 6 for example:
1. When there is no global spare disk or dedicated spare disk in the system, controller 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.
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".
If this disk is not belonging to any existing RG, it would be FR (Free) disk and the system will
start Auto-Rebuild.
If user only removes the failed disk and plugs the same failed disk in the same slot again, the
auto-rebuild will start running. But rebuilding in the same failed disk may impact customer
data if the status of disk is unstable. Sans Digital suggests all customers not to rebuild in the
failed disk for better data protection.
2. When there is enough global spare disk(s) or dedicated spare disk(s) for the degraded array,
controller starts Auto-Rebuild immediately. And in RAID 6, if there is another disk failure
occurs during rebuilding, controller will start the above Auto-Rebuild process as well. Auto-
Rebuild feature only works at that the status of RG is "Online". It will not work at "Offline".
Thus, it will not conflict with the "Roaming".
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 completely one.
Tips
"Set dedicated spare" is not available if there is no RG or only RG of RAID 0, JBOD,
because user can not set dedicated spare disk to RAID 0 & JBOD.
Sometimes, rebuild is called recover; they are the same meaning. The following table is the relationship
between RAID levels and rebuild.
RAID 0 Disk striping. No protection for data. RG fails if any hard drive fails or unplugs.
RAID 1 Disk mirroring over 2 disks. RAID 1 allows one hard drive fails or unplugging.
Need one new hard drive to insert to the system and rebuild to be completed.
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