Tuning the Storage Subsystem - Expert Oracle RAC Performance Diagnostics and Tuning - page 360

DISK A DISK C DISK D DISK E DISK F DISK G

DISK H

DISK B

DATA 04

DATA 01 DATA 01 DATA 02 DATA 02 DATA 03 DATA 03 DATA 04

DATA 11
DATA 21

DATA 11
DATA 21

DATA 12
DATA 22

DATA 12
DATA 22

DATA 13
DATA 23

DATA 13
DATA 23

DATA 14
DATA 24

DATA 14
DATA 24

Figure 12-6. RAID10

■ raiD configurations can be implemented at the software level or at the hardware level. Software-level raiDs
mean multiple writes at the same time. however, in the case of hardware-level raiDs, writes happen to one of the
mirrored volumes and are copied to the other mirrored volumes at the controller level.

Note

raiD10 is the most common type of raiD solution deployed for oracle databases. the mirroring feature of raiD that can
be implemented at the hardware level, called a hardware raiD, is available with raiD10.

RAID5
Under RAID5, parity calculations provide data redundancy, and the parity is stored with the data. This means that the
parity is distributed across the number of drives configured in the volume. ( Parity is a term for error checking). Parity
algorithms contain error correction code (ECC) capabilities, which calculate parity for a given stripe or chunk of data
within a RAID volume. If a single drive fails, the RAID5 array can reconstruct that data from the parity information
held on other disks.
Figure 12-7 illustrates the physical placement of stripes (DATA 01 through DATA 04) with their corresponding
parities distributed across the five disks in the volume:

DISK D DISK E

DISK B DISK C

DISK A

DATA 04
Parity 02
DATA 23

Parity 01
DATA 14
DATA 24

DATA 01
DATA 11
DATA 21

DATA 02
DATA 12
DATA 22

DATA 03
DATA 13
Parity 03

DATA 33 DATA 34

DATA 31 Parity 04 DATA 32

Figure 12-7. RAID5

Figure 12-7 is a four-way striped RAID5 illustration of where data and parity are distributed.
RAID5 is not recommended for OLTP because of its extremely poor performance doing small writes at high
concurrency levels. This is because the continuous processes of reading a stripe, calculating the new parity, and
writing the stripe back to the disk (with new parity) make write-time significantly longer. RAID5 computes and writes