Arrays; Fault Tolerance - HP StoreEasy 1000 Administrator's Manual

Arrays

See Figure 42 (page
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 HPE StoreEasy 1000 Storage model, array configuration may not
be possible or necessary.
Figure 42 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 43 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 Smart 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.

Fault tolerance

Drive failure, although rare, is potentially catastrophic. For example, using simple striping as
shown in Figure 43 (page
same array, and hence to data loss.
To protect against data loss from hard drive failure, HPE StoreEasy 1000 Storage must be
configured with fault tolerance.
The table below summarizes the important features of the different kinds of RAID supported by
the Smart Array controllers. The decision chart in the following table can help determine which
option is best for different situations.
117). With HPE Smart Array controller installed in the system, the capacity
117), failure of any hard drive leads to failure of all logical drives in the
Figure 43 (page 117).
Storage management elements 117