AMCC 720-0138-00 manual About Initialization, Initialization of Different RAID Types

Background Tasks

About Initialization

For 3ware SATA RAID controllers, initialize means to put the redundant data on the drives of redundant units into a known state so that data can be recovered in the event of a disk drive failure. For RAID 1 and 10, initialization copies the data from the lower port to the higher port. For RAID 5, initialization calculates the RAID 5 parity and writes it to disk. This is sometimes referred to as background initialization or resynching, and does not erase user data.

You can partition, format, and use the unit safely while it is initializing. The unit is fully fault-tolerant while the initialization takes place. That is, if the unit degrades before the initialization is complete, the data will remain intact.

Although you can use the unit while it is being initialized in the background, initialization does slow I/O performance until completed. You can adjust how much initialization will slow performance by setting the rate at which it occurs. (See “Setting Background Task Rate” on page 75.) You can also postpone initialization until a scheduled time. (See “Scheduling Background Tasks” on page 76).

Note: Units will be automatically initialized using background initialization when they are verified for the first time. (Verification requires that the units have been previously initialized.) This will not affect the data on the drives, and the units will perform normally, although performance will be slowed until the initialization and verification are completed.

Initialization of Different RAID Types

Information about initialization for each of the different RAID types is described below.

Initialization of RAID 0 Units

RAID 0 units do not need to be initialized and cannot be initialized. RAID 0 units are immediately available for use with full performance when created.

Initialization of RAID 5 Units

RAID 5 units will be automatically initialized the first time they are verified.

Regardless of the size, all RAID 5 units are fully fault tolerant upon creation. These configurations use a specialized scheme for writing to the unit, which does not have to be valid to provide fault tolerance.

RAID 5 units with 3 or 4 disks do not need to be initialized to have full performance upon creation.

www.3ware.com 69