About Initialization

Some RAID levels must be initialized for best performance. (For specifics, see Initialization of Different RAID Types.) Initialization can take place before the units are put into service (foreground initialization) or while the units are being used (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. Background initialization uses an algorithm to perform initialization and does not rewrite existing data.

Foreground Versus Background Initialization

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 does not write zeroes to the drives or harm your data, so you can partition, format, and use the unit safely. For the 9000 series, the unit is fully fault-tolerant while the initialization takes place. That is, if the array 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. (For more information, see Setting Background Task Rate.) You can also postpone initialization until a scheduled time. (For details, see Scheduling Background Tasks).

Note: Units that do not need to be immediately initialized for full performance will be automatically initialized using background initialization if they are ever verified. (Verification requires that the unit 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.

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Related Topics

Initialization of Different RAID Types

Auto Initialization After Power Failure

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