Fault-Tolerance Methods; Raid 0-Data Striping; Advantages; Disadvantages - HP StorageWorks 4000s - NAS Administration Manual

Storage Management Overview

Fault-Tolerance Methods

Different RAID (redundant array of independent disks) types use different methods of striping
the arrays and different ways of writing data and parity to the drives to offer a variety of fault
tolerance and capacity usage. The RAID methods supported by the NAS server include:
Further protection against data loss can be achieved by assigning an online spare to an array.
This hard drive contains no data and is contained within the same storage subsystem as the
other drives in the array. When a hard drive in the array fails, the controller can then
automatically rebuild information that was originally on the failed drive onto the online spare.
This quickly restores the system to full RAID level fault tolerance protection.
Note:
Virtual Arrays and is equivalent to ADG.
These fault tolerance methods are discussed in the following paragraphs.
RAID 0—Data Striping
This configuration provides striping of the array to improve read and write performance, but
offers no redundancy of data and therefore no protection against data loss when a drive fails.
However, RAID 0 is useful for rapid storage of large amounts of noncritical data (for printing
or image editing, for example) or when cost is the most important consideration.
When creating RAID 0 arrays, carefully consider how many drives to include in the array.
Statistically, the chance of a drive failure increases with each additional drive that is included
in an array. Based upon laboratory testing, HP recommends including no more than 7 drives in
a RAID 0 array.
See

Advantages

Disadvantages

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RAID 0—Data Striping only, no fault tolerance
RAID 1+0—Drive Mirroring and striping
RAID 5—Distributed Data Guarding
RAID ADG—Advanced Data Guarding (ADG)
The ADG feature is available only with the MSA1000. RAID 5DP is available only with HP
Figure 26 for an illustration of the data striping technique.
Highest performance method for reads and writes
Lowest cost per unit of data stored
All drive capacity is used to store data; none is used for fault tolerance
All data on logical drive is lost if a hard drive fails
Cannot use an online spare
Data can only be preserved by being backed up to external media
NAS 4000s and 9000s Administration Guide