HP Smart Array 6i Controller and 128MB BBWC - Manual (Page 41)

Drive Arrays and Fault-Tolerance Methods 41
For data in the logical drive to be readable, the data block sequence must be the
same in every stripe. This sequencing process is performed by the array
controller, which sends the data blocks to the drive write heads in the correct
order.
A natural consequence of the striping process is that each physical drive in a
given logical drive will contain the same amount of data. If one physical drive
has a larger capacity than other physical drives in the same logical drive, the
extra capacity is wasted because it cannot be used by the logical drive.
The group of physical drives containing the logical drive is called a drive array,
or just array (denoted by An in the figure). Because all the physical drives in an
array are commonly configured into just one logical drive, the term array is often
used as a synonym for logical drive. However, an array can contain several
logical drives, each of a different size.
Each logical drive in an array is distributed across all of the physical drives
within the array. A logical drive can also extend across more than one port on the
same controller, but it cannot extend across more than one controller.
Drive failure, although rare, is potentially catastrophic. For arrays that are
configured as shown in the previous figure, failure of any physical drive in the
array causes every logical drive in the array to suffer irretrievable data loss. To
protect against data loss due to physical drive failure, logical drives are
configured with fault tolerance ("Fault-Tolerance Methods" on page
42 ).
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