HP StoreEasy 3830 Gateway Storage/S-Buy User Manual download pdf (Page 52)

Fault tolerance

Drive failure, although rare, is potentially catastrophic. For example, using simple striping as shown

in Figure 26, failure of any hard drive leads to failure of all logical drives in the same array, and

hence to data loss.

To protect against data loss from hard drive failure, storage systems 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 the following table can help determine which option is

best for different situations.

Table 10 Summary of RAID methods

RAID 6 (ADG)

RAID 5 Distrib-

uted Data

Guarding

RAID 1+0 Mir-

roring

RAID 0 Strip-

ing (no fault

tolerance)

Storage system dependent14N/AN/A

Maximum number of hard

drives

YesYesYesNo

Tolerant of single hard

drive failure?

Yes (two drives can fail)No

If the failed

drives are not

mirrored to

each other

Tolerant of multiple simul-

taneous hard drive fail-

ures?

Online spares

Further protection against data loss can be achieved by assigning an online spare (or hot spare) to

any configuration except RAID 0. 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. However, unless RAID

Advanced Data Guarding (ADG) is being used, which can support two drive failures in an array, in

the unlikely event that a third drive in the array should fail while data is being rewritten to the spare,

the logical drive still fails.

Logical storage elements

Logical storage elements consist of those components that translate the physical storage elements to

file system elements. The storage system uses the Window Disk Management utility to manage the

various types of disks presented to the file system. There are two types of LUN presentation: basic

disk and dynamic disk. Each of these types of disk has special features that enable different types of

management.

Logical drives (LUNs)

While an array is a physical grouping of hard drives, a logical drive consists of components that

translate physical storage elements into file system elements.

Storage management overview52

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