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8.1.2 RAID 1
This level provides adequate security for your data, because the data is copied to another hard disk
1:1. This is known as hard disk mirroring. If a disk is destroyed, a copy of its contents is available on
another mirrored disk. All disks except one could be damaged without endangering your data.
However, if damage is not detected, damaged data might be mirrored to the correct disk and the data
is corrupted that way. The writing performance suffers a little in the copying process compared to
when using single disk access (10 to 20 % slower), but read access is significantly faster in
comparison to any one of the normal physical hard disks, because the data is duplicated so can be
scanned in parallel. RAID 1 generally provides nearly twice the read transaction rate of single disks
and almost the same write transaction rate as single disks.
8.1.3 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 rarely used.
8.1.4 RAID 4
Level 4 provides block-level striping just like Level 0 combined with a dedicated parity disk. If a
data disk fails, the parity data is used to create a replacement disk. However, the parity disk might
create a bottleneck for write access. Nevertheless, Level 4 is sometimes used.
8.1.5 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 possible to avoid
the risk of losing data.
8.1.6 Nested RAID Levels
Several other RAID levels have been developed, such as RAIDn, RAID 10, RAID 0+1, RAID 30,
and RAID 50. Some of them being proprietary implementations created by hardware vendors. These
levels are not very widespread, and are not explained here.
8.2 Soft RAID Configuration with YaST
The YaST soft RAID configuration can be reached from the YaST Expert Partitioner. This
partitioning tool enables you to edit and delete existing partitions and create new ones that should be
used with soft RAID.
You can 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 use only partitions of the same size because each segment can contribute only
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SLES 11: Storage Administration Guide
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