HP StorageWorks X1800sb Network Storage Blade - Manual (Page 21)

• Include the appropriate number of physical drives in the arrays to create logical storage elements
of desired sizes.
Arrays
See Figure 2 . With an array controller installed in the system, the capacity of several physical drives
(P1–P3) can be logically combined into one or more logical units (L1) called arrays. When this is
done, the read/write heads of all the constituent physical drives are active simultaneously, dramatically
reducing the overall time required for data transfer.
NOTE:
Depending on the storage system model, array configuration may not be possible or necessary.
Figure 2 Configuring arrays from physical drives
Because the read/write heads are simultaneously active, 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 3 .
Figure 3 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 contains the
same number of data blocks.
NOTE:
If one hard drive has a larger capacity than other hard drives in the same array, the extra capacity
is wasted because it cannot be used by the array.
X1800sb and X3800sb Network Storage Blade 21