User manual

Chapter 4 Advanced operation
4.1 Rebuild
If one of the physical disk o n the VG which was set to a protected RAID level
(e.g.: RAID 3, RAID 5, or RAID 6) has FAILED or has been unplugged/removed,
then, the VG status is changed to degraded mode. The system will
search/detect for a spare disk to rebuild the degraded VG. It will look for a
dedicated spare disk first and if none is found, it will check if a global spare disk
has been set up and use this disk for rebuild.
ISC8P2G-S supports Auto-Rebuild function. If the RAID level set on the VG is
protected, such as RAID 3, RAID 5, RAID 6, and etc, ISC8P2G -S starts Auto-
Rebuild as shown on the scenario below:
Take RAID 6 for example:
1. When there is no global spare disk or dedicated spare disk on the system ,
ISC8P2G-S 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 automat ically.
a. If the new added disk is not clean (with data on it), it would be marked
as RS (reserved) and the system will not start "auto -rebuild".
b. If this disk does not belong to any existing VG, it would be FR (Free)
disk and the system will start Au to-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. But rebuilding th e array using the
same failed disk may impact customer data later because of the unstable disk
status. We suggest all customers not to rebuild the array using 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, ISC8P2G -S starts Auto-Rebuild immediately. A nd in RAID 6, if
there is another disk failure happening during the time of rebuilding, ISC8P2G -S
will start the above Auto -Rebuild scenario as well. And the Auto -Rebuild feature
only works at "RUNTIME". It will not work during downtime. Thus, it will not
conflict with the “Roaming” function.
In degraded mode, the status of VG is “DG”.