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HP StorageWorks 2000 Modular Smart Array Reference Guide (481599-003, August 2008)

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Appendix B RAID Levels 249
RAID Level Descriptions
RAID levels are numbered from 0 through 6; a higher RAID level does not
necessarily indicate a higher level of performance or fault tolerance. The RAID
controllers support RAID levels that have proven to be the most useful for RAID
applications: RAID 0, 1, 10, 3, 5, 50, and 6. You can use Non-RAID for a virtual
disk that will have a single drive and not need the data redundancy or performance
benefits of RAID.
RAID 0
In a RAID 0 virtual disk, data is distributed, or striped, across the disk drives in the
virtual disk. The virtual disk appears to the host as one large disk with a capacity
approximately equal to the combined capacity of the disk drives. Because multiple
reads and writes can be handled in parallel, the I/O performance of the virtual disk
is much better than that of a single disk drive.
RAID 0 virtual disks do not store redundant data, so they are not true RAID
applications. If one disk drive fails, the entire virtual disk fails and all virtual disk
data is lost. The fault tolerance of a RAID 0 virtual disk, therefore, is less than that
of any single disk drive in the virtual disk. The term RAID 0 is widely used for
these virtual disks, however, because they are conceptually similar to true RAID
applications.
RAID 1, RAID 10
In RAID 1 and RAID 10 virtual disks (commonly called mirrored virtual disks),
disk drives are paired, with both disk drives in a pair containing the same data.
When data is written to a mirrored virtual disk, it is written twice—once to each
disk drive in the pair. A RAID 1 virtual disk has only one set of paired disk drives.
A RAID 10 virtual disk has multiple pairs, across which data is striped.
The read performance of RAID 1 virtual disks can be much better than that of a
single disk drive, while the write performance is slightly lower. In RAID 10 virtual
disks, both read performance and write performance are better than those of a single
disk drive.