Novell LINUX ENTERPRISE SERVER 10 SP2 - INSTALLATION AND ADMINISTRATION Installation Manual page 143

RAID 2 and RAID 3
These are not typical RAID implementations. Level 2 stripes data at the bit level
rather than the block level. Level 3 provides byte-level striping with a dedicated
parity disk and cannot service simultaneous multiple requests. Both levels are only
rarely used.
RAID 4
Level 4 provides block-level striping just like Level 0 combined with a dedicated
parity disk. In the case of a data disk failure, the parity data is used to create a re-
placement disk. However, the parity disk may create a bottleneck for write access.
Nevertheless, Level 4 is sometimes used.
RAID 5
RAID 5 is an optimized compromise between Level 0 and Level 1 in terms of
performance and redundancy. The hard disk space equals the number of disks used
minus one. The data is distributed over the hard disks as with RAID 0. Parity blocks,
created on one of the partitions, are there for security reasons. They are linked to
each other with XOR, enabling the contents to be reconstructed by the corresponding
parity block in case of system failure. With RAID 5, no more than one hard disk
can fail at the same time. If one hard disk fails, it must be replaced as soon as pos-
sible to avoid the risk of losing data.
Other RAID Levels
Several other RAID levels have been developed (RAIDn, RAID 10, RAID 0+1,
RAID 30, RAID 50, etc.), some of them being proprietary implementations created
by hardware vendors. These levels are not very widespread, so are not explained
here.
7.2.2 Soft RAID Configuration with YaST
The YaST soft RAID configuration can be reached from the YaST Expert Partitioner,
described in Section 8.5.7, "Using the YaST Partitioner" (page 155). This partitioning
tool enables you to edit and delete existing partitions and create new ones that should
be used with soft RAID. There, create RAID partitions by first clicking Create > Do
not format then selecting 0xFD Linux RAID as the partition identifier. For RAID 0 and
RAID 1, at least two partitions are needed—for RAID 1, usually exactly two and no
more. If RAID 5 is used, at least three partitions are required. It is recommended to
take only partitions of the same size. The RAID partitions should be stored on different
hard disks to decrease the risk of losing data if one is defective (RAID 1 and 5) and to
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