System information

two drives in the array. This complex parity scheme creates a significantly higher CPU
burden on software RAID devices and also imposes an increased burden during write
transactions. As such, level 6 is considerably more asymmetrical in performance than levels
4 and 5.
The total capacity of a RAID level 6 array is calculated similarly to RAID level 5 and 4,
except that you must subtract 2 devices (instead of 1) from the device count for the extra
parity storage space.
Level 10
This RAID level attempts to combine the performance advantages of level 0 with the
redundancy of level 1. It also helps to alleviate some of the space wasted in level 1 arrays
with more than 2 devices. With level 10, it is possible to create a 3-drive array configured to
store only 2 copies of each piece of data, which then allows the overall array size to be 1.5
times the size of the smallest devices instead of only equal to the smallest device (like it
would be with a 3-device, level 1 array).
The number of options available when creating level 10 arrays (as well as the complexity of
selecting the right options for a specific use case) make it impractical to create during
installation. It is possible to create one manually using the command line md ad m tool. For
details on the options and their respective performance trade-offs, refer to man md .
Lin ear RAID
Linear RAID is a simple grouping of drives to create a larger virtual drive. In linear RAID, the
chunks are allocated sequentially from one member drive, going to the next drive only when
the first is completely filled. This grouping provides no performance benefit, as it is unlikely
that any I/O operations will be split between member drives. Linear RAID also offers no
redundancy and, in fact, decreases reliability — if any one member drive fails, the entire
array cannot be used. The capacity is the total of all member disks.
17.3. Linux RAID Subsyst ems
RAID in Linux is composed of the following subsystems:
Linux Hardware RAID controller drivers
Hardware RAID controllers have no specific RAID subsystem in Linux. Because they use special
RAID chipsets, hardware RAID controllers come with their own drivers; these drivers allow the system
to detect the RAID sets as regular disks.
mdraid
The md rai d subsystem was designed as a software RAID solution for Linux; it is also the preferred
solution for software RAID under Linux. This subsystem uses its own metadata format, generally
referred to as native md rai d metadata.
md rai d also supports other metadata formats, known as external metadata. Red Hat Enterprise
Linux 6 uses md rai d with external metadata to access ISW / IMSM (Intel firmware RAID) sets.
md rai d sets are configured and controlled through the md ad m utility.
Linux Hard ware RAID cont roller drivers
129