Chapter 4 Advanced operation
4.1 Rebuild
If one physical disk of the VG 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 VG is changed to degraded mode,
the system will search/detect spare disk to rebuild the degraded VG to a complete one. It will detect
dedicated spare disk as rebuild disk first, then global spare disk.
Sans Digital AR108X SAS RAID
supports 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 VG automatically.
If the new added disk is not clean (with other VG 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 VG, 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. 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 same failed disk.
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 VG is "Online". It will not work at “Offline”. Thus, it will not conflict with
the “Roaming”.
3. In degraded mode, the status of VG is “Degraded”. When rebuilding, the status of VG/UDV will be
“Rebuild”, the column “R%” in UDV will display the ratio in percentage. After complete rebuilding, the
status will become “Online”. VG will become completely one.
Tips :
“Set dedicated spare”
is not available if there is no VG or only VG 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. VG 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.
N-way mirror
Extension to RAID 1 level. It has N copies of the disk. N-way mirror allows N-1 hard
drives failure or unplugging.
Advanced operation
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