Drive Arrays and Fault Tolerance
C-2
Compaq Smart Array 5i Plus Controller and Battery Backed Write Cache Enabler User Guide
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
With an array controller installed in the system, the capacity of several physical
drives can be combined into one or more virtual units called
logical drives
(also
called logical volumes). Then, the read/write heads of all the constituent physical
drives are active simultaneously, reducing the total time required for data transfer.
L1
P1
P2
P3
Figure C-2: Physical drives configured into a logical
drive (L1)
Because the read/write heads are active simultaneously, the same amount of data is
written to each drive during any given time interval. Each unit of data is called a
block,
and over all the physical drives in a logical drive the blocks form a set of data
stripes
(see Figure C-3).
