Veritas Storage Foundation™ for Oracle 5.0.1 Administrator's Guide

About disk groups
A disk group is a collection of disks that share a common configuration (for
example, configuration objects that belong to a single database). We recommend
creating one disk group for each database.
You can move a disk group and its components as a unit from one host to another
host. For example, you can move volumes and file systems that belong to the same
database and are created within one disk group as a unit. You must configure a
given volume from disks belonging to one disk group.
In releases before Veritas Storage Foundation 4.0 for Oracle, the default disk
group was rootdg. For VxVM to function, the rootdg disk group had to exist and
it had to contain at least one disk. This requirement no longer exists, and VxVM
can work without any disk groups configured (although you must set up at least
one disk group before you can create any volumes of other VxVM objects).
About volume layouts
A Redundant Array of Independent Disks (RAID) is a disk array in which a group
of disks appears to the system as a single virtual disk or a single volume. VxVM
supports several RAID implementations, as well as spanning.
The following volume layouts are available to satisfy different database
configuration requirements:
■ Spanning and concatenation
■ Striping (RAID-0)
■ Mirroring (RAID-1)
■ Mirrored-Stripe Volumes (RAID-0+1)
■ Striped-Mirror Volumes (RAID-1+0)
■ RAID-5
Caution: Spanning or striping a volume across multiple disks increases the
chance that a disk failure will result in failure of that volume. Use mirroring
or RAID-5 to substantially reduce the chance of a single volume failure caused
by a single disk failure.
How spanning and concatenation work
Concatenation maps data in a linear manner onto one or more subdisks in a plex.
To access all of the data in a concatenated plex sequentially, data is first accessed
23Introducing Veritas Storage Foundation for Oracle
How Veritas Volume Manager works