HP 345646-001 - StorageWorks NAS 2000s External Storage Server Administration Manual page 46

Storage Management Overview
Figure 21: Configuring the physical drives into an array dramatically improves read/write
efficiency
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 termed a block. The blocks form
a set of data stripes over all the hard drives in an array, as shown in
Figure 22: RAID 0 (data striping) (S1-S4) of data blocks (B1-B12)
For data in the array to be readable, the data block sequence within each stripe must be the
same. 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 hard drive in a given array will
contain the same number of data blocks.
Note:
capacity is wasted because it cannot be used by the array.
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P1 P2
S1
B1 B2
S2
B4 B5
S3
B7
B8
S4
B10 B11
If one hard drive has a larger capacity than other hard drives in the same array, the extra
L1
P3
B3
B6
B9
B12
Figure 22.
NAS 2000s Administration Guide