Veritas Storage Foundation™ for Oracle 5.0.1 Administrator's Guide

In general, for most OLTP databases, use the default stripe unit size of 64 K or
smaller for striped volumes and 16 K for RAID-5 volumes.
How to choose between mirroring and RAID-5
VxVM provides two volume configuration strategies for data redundancy:
mirroring and RAID-5. Both strategies allow continuous access to data in the event
of disk failure. For most database configurations, we recommend using mirrored,
striped volumes. If hardware cost is a significant concern, but having higher data
availability is still important, use RAID-5 volumes.
RAID-5 configurations have certain performance implications you must consider.
Writes to RAID-5 volumes require parity-bit recalculation, which adds significant
I/O and CPU overhead. This overhead can cause considerable performance
penalties in online transaction processing (OLTP) workloads. If the database has
a high read ratio, however, RAID-5 performance is similar to that of a striped
volume.
Volume configuration guidelines
Follow these guidelines when selecting volume layouts:
■ Put the database log files on a file system created on a striped and mirrored
(RAID-0+1) volume separate from the index or data tablespaces. Stripe multiple
devices to create larger volumes if needed. Use mirroring to improve reliability.
Do not use VxVM RAID-5 for redo logs.
■ When normal system availability is acceptable, put the tablespaces on file
systems created on striped volumes for most OLTP workloads.
■ Create striped volumes across at least four disks. Try to stripe across disk
controllers. For sequential scans, do not stripe across too many disks or
controllers. The single thread that processes sequential scans may not be able
to keep up with the disk speed.
■ For most workloads, use the default 64 K stripe-unit size for striped volumes
and 16 K for RAID-5 volumes.
■ When system availability is critical, use mirroring for most write-intensive
OLTP workloads. Turn on Dirty Region Logging (DRL) to allow fast volume
resynchronization in the event of a system crash.
■ When system availability is critical, use RAID-5 for read-intensive OLTP
workloads to improve database performance and availability. Use RAID-5 logs
to allow fast volume resynchronization in the event of a system crash.
■ For most decision support system (DSS) workloads, where sequential scans
are common, experiment with different striping strategies and stripe-unit
Setting up databases
About selecting a volume layout
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