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
A
n
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 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.
Hardware issues
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