Avago Technologies 3ware SAS 9750-16i4e - Manual (Page 159)

Background Tasks
www.lsi.com/channel/products 147
When initializing is done after booting to the operating system, the process of
initializing takes longer than it does if initialization is done by writing zeroes
to the unit in the BIOS. Consequently, it will be a longer period of time until
the performance of the unit is fully optimal.
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 162.) You can also
postpone initialization until a scheduled time. (See “Scheduling Background
Tasks” on page 163).
Initialization of Different RAID Types
Information about initialization for each of the different RAID types is
described below and summarized in Table 12 on page 148.
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, RAID 6, and RAID 50 Units
RAID 5 units with three or four drives will be automatically initialized the
first time they are verified.
Regardless of the size, all 9000-series RAID 5, RAID 6, and RAID 50 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.
Performance of the following types of units will improve after the unit has
been initialized: RAID 6, RAID 5 units with 5 or more disks, and RAID 50
units with 2 subunits of 5 or 6 disks. For these configurations, initialization
begins automatically after you create them. If you create them in 3BM using
the default foreground initialization method, zeroes are written to all unit
members before booting to the operating system. If you create them through
3DM2, you will boot to the operating system and the RAID 5 parity is then
calculated and written to disk, keeping any data in the unit intact.
RAID 5 units with 3 or 4 disks do not need to be initialized to have full
performance upon creation. It is okay that 3 or 4 disk RAID 5 units are not
Note: Units that are not initialized through 3BM are 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.