Installation manual

43 ATTO Technology Inc. ATTO Utilities Installation and Operation Manual
Failure Scenario Table
RAID Groups cannot be accessed normally when their member disks fail, and the RAID Group is marked
OFFLINE. RAID Groups of different RAID levels are marked OFFLINE for different reasons, as follows:
Exhibit 1.4.1--17 Failure Scenarios and Recovery Methods
Drive Replacement on a Failure Condition
Replacing RAID Group Member Drives as
Soon as They Fail
With parity and redundancy RAID levels, the RAID
Group can withstand the loss of one member, and the
data is still valid and accessible. In this case, the RAID
Group goes into DEGRADED mode and uses parity or
redundancy to generate the data. Although the RAID
Group is fully operational, the RAID Group is at risk
because if any other drive fails, data integrity is called
into question.
A Warning about Drive Replacement
A very common reason that an array goes from
DEGRADED mode to OFFLINE mode is when the
wrong drive is replaced. By pulling out a perfectly good
drive, a double-drive fault occurs and there are
insufficient drives to generate data. The following
procedure is very important when you are considering
removing a failed drive, to ensure the correct drive is
pulled.
RAID Level
Reason(s) for
being marked
OFFLINE
Recovery Method
JBOD and RAID 1 Any drive failure.
See Faults on Critical Number of Drives
on
page 49
RAID 1 and RAID 10
Error during
rebuild
See Recovery from Failed Rebuild
on page 47
Mistaken
replacement of a
good drive when its
mirror has failed
See Recovery from Replacement of Wrong
Drive on page 46
RAID 4 and RAID 5
Errors on two or
more drives
See Faults on Critical Number of Drives
on
page 49
Error during
rebuild
See Recovery from Failed Rebuild
on page 47
Mistaken
replacement of a
good drive when
another member
of the RAID Group
has failed
See Recovery from Replacement of Wrong
Drive on page 46
RAID 6
Errors on three or
more drives
See Faults on Critical Number of Drives
on
page 49
Error during
rebuild
See Recovery from Failed Rebuild
on page 47
Mistaken
replacement of
good drive(s)
when other
members of the
RAID Group have
failed
See Recovery from Replacement of Wrong
Drive on page 46