Hp StorageWorks 1510i Modular Smart Array Uživatelský manuál stáhnout pdf (Strana 149)

Table 5 RAID 5 features

Advantages Disadvantages

High read performance. Relatively low write performance.

No loss of data if one physical drive fails.

Lossofdataifaseconddrivefailsbeforedatafrom

the ﬁrst failed drive is rebuilt.

More usable drive capacity than RAID 1+0, because

parity information requires the storage space

equivalent to one physical drive.

RAID 6—advanced data guarding

RAID 6 (also called RAID ADG) is similar to RAID 5, because both methods generate and store parity

information to protect against data loss caused by drive failure. With RAID 6, however, two different

sets of parity data are distributed across the physical drives, allowing data to be preserved even if

two drives fail. Each set of parity data uses up a capacity equivalent to that of one of the constituent

drives, as shown in Figure 8.

P5,6

Q7,8

D1 D2 D3 D4

P3,4

Q5,6

P1,2

Q3,4

P7,8

Q1,2

15317

Figure 8 RAID 6 array, with four physical hard drives (D1, D2, D3, D4) showing

distributed parity information (Px,y)(Qx,y)

This method is most useful when data loss is unacceptable, but cost is also an important factor. The

probability that data loss will occur when arrays are conﬁgured with RAID 6 is less than when they

are conﬁgured with RAID 5.

Table 6 RAID 6 features

Advantages Disadvantages

High read performance.

Relatively low write performance (lower than RAID 5),

because of the need to create two sets of parity data.

High data availability—Any two drives can fail

without loss of critical data.

More drive capacity is usable than with RAID

1+0—Parity information requires only the storage

equivalent to two physical drives.

Comp

arison of RAID Methods

Tabl

e7summarizes important features of the different RAID levels.

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