Drive Arrays and Fault Tolerance
Compaq Smart Array 5i Plus Controller and Battery Backed Write Cache Enabler User Guide
C-3
COMPAQ CONFIDENTIAL
Writer: Amy L. Laffitte File Name: l-appc Drive Arrays and Fault Tolerance
Codename: Executor Part Number: 266328-001 Last Saved On: 4/18/02 2:51 PM
S1
S2
S3
S4
B1
B4
B7
B2
B5
B8
B11
B10
B12
B6
B3
B9
Figure C-3: Data striping (S1-S4) of data blocks B1-B12
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
simply
array.
Since all the physical drives in an array are commonly configured into
just one logical drive, the term array is also often used as a synonym for logical drive.
However, an array can contain several logical drives, each of a different size (see
Figure C-4).
