VERITAS Volume Manager 4.1 Administrator's Guide

Understanding VERITAS Volume Manager
Volume Layouts in VxVM
Chapter 122
Striping (RAID-0)
NOTE You may need an additional license to use this feature.
Striping (RAID-0) 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.
Striping maps data so that the data is interleaved among two or more
physical disks. A striped plex contains two or more subdisks, spread out
over two or more physical disks. Data is allocated alternately and evenly
to the subdisks of a striped plex.
The subdisks are grouped into “columns,” with each physical disk limited
to one column. Each column contains one or more subdisks and can be
derived from one or more physical disks. The number and sizes of
subdisks per column can vary. Additional subdisks can be added to
columns, as necessary.
CAUTION Striping a volume, or splitting a volume across multiple disks, increases
the chance that a disk failure will result in failure of that volume.
If five volumes are striped across the same five disks, then failure of any
one of the five disks will require that all five volumes be restored from a
backup. If each volume is on a separate disk, only one volume has to be
restored. (As an alternative to striping, use mirroring or RAID-5 to
substantially reduce the chance that a single disk failure results in
failure of a large number of volumes.)
Data is allocated in equal-sized units (stripe units) that are interleaved
between the columns. Each stripe unit is a set of contiguous blocks on a
disk. The default stripe unit size (or width) is 64 kilobytes.