Multiple Disks Failed - Theory - Bosch DIVAR IP 6000 1U Installation Manual

38 en | Appendix
Basically, the RAID controller writes the raidconfiguration - information (COD = configuration-
on-disk) in an only field on each disk managed by the controller. The data area of a disk is
never used by this, no matter, how often you write and delete the RAID configuration. "New"
or "Clear" Configuration deletes the COD, if available.
"Save Configuration" saves the new COD. "Initialize" deletes the Disk Data (OS).
The data area can only be deleted with a "fast" or "full" initialization; as long as an initialization
is omitted, the OS file system is still there. But OS only boots, if the original RAID
configuration is restored (if no multiple hardware damage exists).
If, for example, the RAID is deleted accidently (eg. with "clear" or "new configuration" instead
of add),and the configuration is set up exactly (in disk order and stripesize) the same as
before, the data area on the remaining operating system boots again without any problem.
This fact is useful when the RAID (COD) was lost for some reason, but the disks are OK.
5.9.1

Multiple disks failed - theory

If multiple disks have failed (by power failure, backplane error, etc.), it is important to know
the order, which disk failure degraded the RAID (first fail) and which disk ID prevented a
further access to the RAID (second fail).
For instance:
RAID 5 (4 disks) got from rebuild to offline, no Hot Spare
- 2 disks online
2014.01 | V2 | DOC Installation manual
DIVAR IP 6000 1U
Bosch Sicherheitssysteme GmbH