AMCC 3ware 9000 Series, User Manual

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About Background Tasks
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Initialization of RAID 1, RAID 10 will take place automatically the first time
the unit is verified.
Initialization of a RAID 1 unit results in data from one disk (the disk on the
lower channel number) being copied to the other disk. In RAID 10 units, data
from one half of the unit is copied to the other half.
After the initialization, subsequent verifies to a RAID 1 or 10 unit check for
data consistency by comparing the data from one drive (or set of drives) to the
other drive (or set of drives).
Auto Initialization After Power Failure
The 3ware controller detects and handles power failures. This mechanism is
intended to ensure that redundant units have consistent data and parity. When
a redundant unit is unexpectedly shutdown, there is a possibility some data
and parity may be inconsistent. For redundant units, if a unit or sub-unit is
detected to have been shutdown uncleanly, the unit or sub-unit will change its
mode to either ‘Initializing’ or ‘Verifying’.
3ware’s auto-initialization feature determines if this is required. During driver
startup, a flag is set that indicates that the driver loaded. Upon an orderly
shutdown, the flag is rewritten, indicating that there was a clean shutdown.
During the next system power cycle the firmware queries the flag. If there was
a power failure, the flag will indicate that there was not a clean shutdown.
This means that the data on the drives may not be correct.
When the initialization is complete, the unit is guaranteed to be redundant
again. The initialization does not erase user data.
About Rebuilds
Fault tolerant RAID units provide data security by duplicating information on
multiple drives.
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RAID 1 and 10 units each use mirroring, where identical data is stored on
two or more drives to protect against drive failure.
„
RAID 5 and 50 units achieve fault tolerance by using a simple (exclusive
OR) function to generate the parity data that is distributed on all drives.
When one of the drives in a fault-tolerant unit is removed, unplugged or fails
on read or write requests, the unit is said to be “degraded.” Rebuilding is the
process by which the RAID unit is made fault tolerant again.
You can still read and write data from a degraded unit, but the unit will not be
fault tolerant until it is rebuilt using the Rebuild feature.