Avago Technologies 3ware SAS 9750-16i4e - Manual (Page 158)

Chapter 8. Maintaining Units
146 3ware SATA+SAS RAID Controller Card Software User Guide, Version 10.2
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. 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 147.) When these units
are created in the BIOS (through 3BM), you can choose to do a foreground
initialization, which will take place before the operating system has loaded, or
a background initialization, which allows you to put the unit in service
immediately, but will slow down the unit performance until it completes. 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 can be run from the BIOS using 3BM. It clears all
existing data from the drives. Foreground initialization can take up to 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 you are creating a unit through 3BM and if immediate access to the unit is
important, select background initialization. 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.
Mac User Note: Foreground initializations are only done in 3BM, which is not
applicable for Mac users.
Note: Drives that support the Write Same feature (SCT) can write to multiple drive
sectors at once, improving initialization time. To take advantage of this feature, all
the drives in the unit must support Write Same.