VERITAS Storage Foundation 4.1 Oracle Administrator's Guide

VERITAS Volume Manager Prerelease 8 September 2005, 8:54am
26 VERITAS Storage Foundation for Oracle Administrator’s Guide
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).
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.
Spanning and Concatenation
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 in the first subdisk from
beginning to end. Data is then accessed in the remaining subdisks sequentially from beginning to
end, until the end of the last subdisk.
The subdisks in a concatenated plex do not have to be physically contiguous and can belong to
more than one VM disk. Concatenation using subdisks that reside on more than one VM disk is
called spanning.
Spanning is useful when you need to read or write data sequentially (for example, reading from or
writing to database redo logs) and there is not sufficient contiguous space.