Fault Tolerance - HP ML110 G1 User Manual

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 5
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:
the same array, the extra capacity is wasted because it cannot be used
by the array.

Fault tolerance

Drive failure, although rare, is potentially catastrophic. For example, in
Figure 5
all logical drives in the same array, and hence to data loss.
To protect against data loss from hard drive failure, storage servers
should be configured with fault tolerance. HP recommends adhering to
RAID 5 configurations.
The table below summarizes the important features of the different kinds
of RAID supported by the Smart Array controllers. The decision chart in
26 Storage Management Overview
S1
B1
S2
B4
S3
B7
S4
B10
RAID 0 (data striping) (S1-S4) of data blocks (B1-B12)
If one hard drive has a larger capacity than other hard drives in
using simple striping, failure of any hard drive leads to failure of
Figure
B3
B2
B6
B5
B8 B9
B11 B12
5.