Veritas Storage Foundation™ for Oracle 5.0.1 Administrator's Guide

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.
How striping plus mirroring (mirrored-stripe or RAID-0+1)
works
VxVM supports the combination of mirroring above striping. The combined layout
is called a mirrored-stripe layout. A mirrored-stripe layout offers the dual benefits
of striping to spread data across multiple disks, while mirroring provides
redundancy of data. For mirroring above striping to be effective, the striped plex
and its mirrors must be allocated from separate disks.
The layout type of the data plexes in a mirror can be concatenated or striped. Even
if only one is striped, the volume is still termed a mirrored-stripe volume. If they
are all concatenated, the volume is termed a mirrored-concatenated volume.
How mirroring plus striping (striped-mirror, RAID-1+0 or
RAID-10) works
VxVM supports the combination of striping above mirroring. This combined layout
is called a striped-mirror layout and mirrors each column of the stripe. If there
are multiple subdisks per column, each subdisk can be mirrored individually
instead of each column. A striped-mirror volume is an example of a layered volume.
Compared to a mirrored-stripe volume, a striped-mirror volume offers the dual
benefits of striping to spread data across multiple disks, while mirroring provides
redundancy of data. A striped-mirror volume enhances redundancy, which makes
it more tolerant of disk failure, and reduces recovery time after disk failure.
For databases that support online transaction processing (OLTP) workloads, we
recommend either mirrored-stripe or striped-mirror volumes to improve database
performance and reliability. For highest availability, we recommend striped-mirror
volumes (RAID 1+0).
How striping with parity (RAID-5) works
RAID-5 provides data redundancy through the use of parity (a calculated value
that the system uses to reconstruct data after a failure). While data is written to
a RAID-5 volume, parity is also calculated by performing an exclusive OR (XOR)
procedure on data. The resulting parity is then written to another part of the
volume. If a portion of a RAID-5 volume fails, the data that was on that portion
of the failed volume can be recreated from the remaining data and the parity.
RAID-5 offers data redundancy similar to mirroring, while requiring less disk
space. RAID-5 read performance is similar to that of striping but with relatively
25Introducing Veritas Storage Foundation for Oracle
How Veritas Volume Manager works