Background Tasks
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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 RAID 10,
initialization copies the data from the lower port to the higher port. For RAID
5, RAID 6, and RAID 50, initialization calculates the RAID 5 parity and
writes it to disk (background initialization). This is sometimes referred to as
background initialization
or
resynching
, and does not erase user data.
Some RAID levels must be initialized for best performance. (For specifics,
see “Initialization of Different RAID Types” on page 144.) When these units
are created in the BIOS (through 3BM), initialization begins immediately.
This type of initialization is referred to as
foreground initialization
, because it
is the primary task being performed on the system, before the operating
system has loaded.
This process erases existing data
, by writing zeroes to all
of the drives in the unit. You can elect to cancel foreground initialization, put
the units into service, and have initialization run in the background, instead.
Foreground Versus Background Initialization
Initialization makes parity information valid. Foreground initialization does
this by simply writing zeroes to all the drives so that they all have the same
values, overwriting any existing data in the process. In contrast, background
initialization uses an algorithm to resynch the parity information on the drives
and does not rewrite existing data.
A foreground initialization is run from the BIOS using 3BM. It clears all
existing data from the drives. Foreground initialization can take several hours,
depending upon the size of the unit. After foreground initialization completes,
you can start the operating system and units will perform at peak efficiency.
If immediate access to the unit is important, you can stop foreground
initialization by pressing
Esc
and booting to the operating system.
Background initialization will then start automatically within about 10
minutes. Background initialization (resynching) does not write zeroes to the
drives or harm your 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.
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 155.) You can also
