HP StorageWorks X3000, System User'S Manual

Page: 49 / 146

• Include the appropriate number of physical drives in the arrays to create logical storage elements
of desired sizes.
Arrays
See Figure 19 . 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 19 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 20 .
Figure 20 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.
HP X1000 and X3000 Network Storage System User Guide 49