Hp D3000 Disk Enclosures User Manual download pdf (Page 23)

RAID methodData redundancyBest practicesSummary

characteristics over a wider range of

application workloads than RAID5.

but uses the most physical disk

space. IMPORTANT: RAID1

uses about 100% more

physical disk space than

RAID0 and 70% more than

RAID5.

Striping and

parity

MediumRAID 50 tolerates one drive failure

in each spanned array without loss

RAID5 protects against failure

of one drive (and failure of

RAID5

of data. RAID 50 requires lessparticular multiple drives).

rebuild time than single RAID 5RAID 50 is a nested RAID

arrays RAID 50 requires a minimum

of six drives.

method that uses RAID 0

striping across RAID 5 arrays.

Striping and

parity

HighRAID6 is most useful when data loss

is unacceptable but cost is also an

RAID6+0 allows administrators

to split the RAID 6 storage

RAID6

important factor. The probability thatacross multiple external boxes.

data loss will occur when an arrayRAID 60 requires a minimum

is configured with RAID6 is less thanof eight drives. RAID 60 is a

it would be if it was configured withnested RAID method that uses

RAID5. However, write performanceRAID 0 block-level striping

is lower than RAID5 because of the

two sets of parity data.

across multiple RAID 6 arrays

with dual distributed parity.

With the inclusion of dual

parity, RAID 60 will tolerate

the failure of two disks in each

spanned array without loss of

data.

Striping and

parity

HighOrganizations implementing a large

drive array should consider RAID 6

Allocates the equivalent of two

parity drives across multiple

RAID6

with

because it can tolerate up to twodrives and allows simultaneousAdvance

simultaneous drive failures without

downtime or data loss.

write operations Distributed

Data Guarding (RAID 5):

Data

Guarding

(ADG) Allocates parity data across

multiple drives and allows

simultaneous write operations.

Drive Mirroring (RAID 1 and

1+0 Striped Mirroring):

Allocates half of the drive array

to data and the other half to

mirrored data, providing two

copies of every file

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 subsystem 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 fails at this time, the array becomes inaccessible and information stored there must

be restored from backup.

Preliminary tasks 23

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