VERITAS Storage Foundation 4.1 Oracle Administrator's Guide

Chapter 1, VERITAS Storage Foundation for Oracle
Prerelease 8 September 2005, 8:54am VERITAS Volume Manager
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Striping (RAID-0)
Striping is a technique of mapping data so that the data is interleaved among multiple physical
disks. Data is allocated in equal-sized units (called stripe units) that are interleaved between the
disks. Each stripe unit is a set of contiguous blocks on a disk. A stripe consists of the set of stripe
units at the same position across all columns. A column is a set of one or more subdisks within a
striped plex.
Striping is useful if you need large amounts of data written to or read from physical disks, and
performance is important. Striping is also helpful in balancing the I/O load from multi-user
applications across multiple disks. By using parallel data transfer to and from multiple disks,
striping significantly improves data-access performance.
When striping across multiple disks, failure of any one disk will make the entire volume unusable.
Mirroring (RAID-1)
Mirroring is a technique of using multiple copies of the data, or mirrors, to duplicate the
information contained in a volume. In the event of a physical disk failure, the mirror on the failed
disk becomes unavailable, but the system continues to operate using the unaffected mirrors. For
this reason, mirroring increases system reliability and availability. A volume requires at least two
mirrors to provide redundancy of data. A volume can consist of up to 32 mirrors. Each of these
mirrors must contain disk space from different disks for the redundancy to be effective.
Striping Plus Mirroring (Mirrored-Stripe or RAID-0+1)
VxVM supports the combination of mirroring with striping. When used together on the same
volume, mirroring plus striping offers the benefits of spreading data across multiple disks while
providing redundancy of data.
Mirrored-stripe volumes have multiple plexes as mirrors, each constructed as a striped plex.
Allocate subdisks used in the same striped plex from separate disks, and use a disk in only one
mirror of a volume.
Mirroring Plus Striping (Striped-Mirror Volumes, RAID-1+0 or RAID-10)
VxVM supports the combination of striping with mirroring. When used together on the same
volume, striping plus mirroring offers the benefits of spreading data across multiple disks while
providing redundancy of data.
Striped-mirror volumes combine striping and mirroring, but the mirroring is done at stripe column
level. In case of failure, this type of volume recovers faster than RAID-0+1 volumes and the
tolerance for disk failure is greater.