faster in comparison to any one of the normal physical hard disks. The reason is
that the duplicate data can be parallel-scanned. Generally it can be said that Level 1
provides nearly twice the read transfer rate of single disks and almost the same
write transfer rate as single disks.
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, exist 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.
RAID 6
To further increase the reliability of the RAID system, it is possible to use RAID 6.
In this level, even if two disks fail, the array still can be reconstructed. With RAID 6,
at least 4 hard disks are needed to run the array. Note that when running as software
raid, this conguration needs a considerable amount of CPU time and memory.
RAID 10 (RAID 1+0)
This RAID implementation combines features of RAID 0 and RAID 1: the data
are rst mirrored in separate disk arrays, which are inserted into a new RAID 0;
type array. In each RAID 1 sub-array, one disk can fail without any damage to the
data. RAID 10 is used for database application where a huge load is expected.
Other RAID Levels
Several other RAID levels have been developed (RAID 2, RAID 3, RAID 4, 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 common
and therefore are not explained here.
3.3.1 Soft RAID Conguration with YaST
The YaST RAID conguration can be reached from the YaST Expert Partitioner, de-
scribed in Section 3.1, “Using the YaST Partitioner” (page 73). This partitioning tool
enables you to edit and delete existing partitions and create new ones to be used with
soft RAID:
Advanced Disk Setup 91
