Chapter 9 Introduction to the Server
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RAID 2
RAID 2 uses common ECC error-correction code to provide fault tolerance.
All drives provide some sort of ECC, so this form of RAID is basically obsolete.
RAID 3
RAID 3 stripes data across multiple drives and stores parity on a separate
drive. Data striping is performed at the byte level. See Figure 9-22.
RAID 4
RAID 4 stripes data across several drives and stores parity on a separate
drive. The main difference between RAID 3 and RAID 4 is RAID 4 stores data in
blocks. The size of the block can vary.
RAID 5
RAID 5 is also called block striping with distributed parity. RAID 5 distributes
parity across all drives rather than writing parity to one drive. It provides fault
tolerance and some increase in read-write data transfer. See Figure 9-23.
Figure 9-21.
RAID 1, or disk
mirroring, provides
a copy of data on two
disk drives.
110100110100110100110100
110100 110100
Same data
Figure 9-22.
RAID 3 writes across
multiple drives with
parity stored on a
separate drive.
110100100101010101010101001010010101010
1110100 0001100 1111000
Data Data Parity
Figure 9-23.
RAID 5 provides
both disk striping
and parity. Parity
and data is
distributed across all
drives.
110100100101010101010101001010010101010
1110100 0001100 1111000
Data
Parity
Data
Data
Data
Parity
Parity
Data
Data