User`s guide

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Appendix B
B. RAID Basics
To assist you in building RAID arrays, this chapter gives a general overview of RAID and
describes various levels of RAID along with JBOD.
RAID Implementations
RAID can be implemented in either dedicated hardware or software running on standard
hardware. Occasionally, you might want hybrid RAID systems—combining software- and
hardware-based solutions.
With software implementations of RAID, the operating system manages the disks through the
normal drive controller (SAS/ SATA). Software RAID can be faster than hardware-based RAID
at the cost of using CPU power. One exception to this is when a dedicated hardware RAID system
has a write cache dedicated to managing the RAID.
A hardware implementation of RAID requires a RAID controller. This may be a PCIe expansion
card or may be a card onboard the system motherboard in some systems. Disks may be of any type:
SAS or SATA. The controller links to the system with a high-speed SCSI or iSCSI connection.
The controller handles the management of disks, including parity calculations (error checking)
which is suited for larger arrays of disks. Hardware RAID tends to have better performance and
makes operating system support easier. Hardware RAID typically supports hot-swapping of
drives as well. Both hardware and software versions support the use of a hot spare, a preinstalled
drive which is used to immediately replace a failed drive.
Some software RAID systems allow building arrays from partitions instead of whole disks.