HP D2600 Manuel d'utilisateur télécharger pdf (Page 27)

RAID meth-

Data redund-

ancy

Best practicesSummary

StripingNone

IMPORTANT: Do not use RAID0

for LUNs if fault tolerance is re-

quired. Consider RAID0 only for

noncritical storage. RAID0 LUNs

provide the best performance for

applications that use random I/O.

RAID0 is optimized for I/O

speed and efficient use of

physical disk capacity, but

provides no data redund-

ancy.

RAID0

MirroringHigh

In general, RAID1 virtual disks

provide better performance char-

acteristics over a wider range of

application workloads than

RAID5.

RAID1 is optimized for data

redundancy and I/O speed,

but uses the most physical

disk space. IMPORTANT:

RAID1 uses about 100%

more physical disk space

than RAID0 and 70% more

than RAID5.

RAID1

Striping and

parity

Medium

RAID5 virtual disks can provide

performance advantages over

RAID1 for some applications that

use sequential I/O. Consider

RAID5 disks for applications with

high sequential I/O of records in

multiples of 8K bytes. The larger

the record size, the greater the

advantage.

RAID5 provides a balance

of data redundancy, I/O

speed and efficient use of

physical disk space.

RAID5

Striping and

parity

High

RAID6 is most useful when data

loss is unacceptable but cost is

also an important factor. The

probability that data loss will oc-

cur when an array is configured

with RAID6 is less than it would

be if it was configured with

RAID5. However, write perform-

ance is lower than RAID5 be-

cause of the two sets of parity

data.

Like RAID5, RAID6 gener-

ates and stores parity inform-

ation to protect against data

loss caused by drive failure.

With RAID6, however, two

different sets of parity data

are used, allowing data to

be preserved if two drives

fail.

RAID6

Disk drive sizes and types

RAID arrays should be composed of disk drives of the same size and performance capability. When

drives are mixed within a disk enclosure, the usable capacity and the processing ability of the entire

storage sub-system is affected. For example, when a RAID array is composed of different sized drives,

the RAID array defaults to the smallest individual drive size, and capacity in the larger drives goes

unused.

Spare disks

Spares are disks that are not active members of any particular array, but have been configured to

be used when a disk in one of the arrays fails. If a spare is present, it will immediately be used to

begin rebuilding the information that was on the failed disk, using parity information from the other

member disks. During the rebuilding process, the array is operating in a reduced state and, unless it

is a RAID6 or RAID1+0 array, it cannot tolerate another disk failure in the same array. If another disk

D2600/D2700 Disk Enclosure User Guide 27

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HP D2600 Manuel d'utilisateur Page 27

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