VERITAS Storage Foundation 4.1 Oracle Administrator's Guide

Chapter 1, VERITAS Storage Foundation for Oracle
Prerelease 8 September 2005, 8:54am VERITAS Volume Manager
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take a long time. You can significantly reduce resynchronization time by using Dirty Region
Logging (DRL) for mirrored volumes or by making sure that RAID-5 volumes have valid RAID-5
logs. However, using logs can slightly reduce the database write performance.
For most database configurations, we recommend using dirty region logs or the RAID-5 logs when
mirrored or RAID-5 volumes are used. It is also advisable to evaluate the database performance
requirements to determine the optimal volume configurations for the databases.
Dirty Region Logging
Dirty Region Logging (DRL), if enabled, speeds the recovery of mirrored volumes after a system
crash. DRL keeps track of the regions that have changed due to I/O writes to a mirrored volume.
DRL uses this information to recover only those portions of the volume that need to be recovered.
Note In VxVM 4.1, if a version 20 data change object (DCO) volume is associated with a volume,
a portion of the DCO volume can be used to store the DRL log. There is no need to create a
separate DRL log for a volume that has a version 20 DCO volume.
SmartSync Recovery Accelerator
SmartSync increases the availability of mirrored volumes by only resynchronizing changed data.
SmartSync reduces the time required to restore consistency, freeing more I/O bandwidth for
business-critical applications.
This feature is applicable only to databases that are configured on raw volumes. If supported by the
database vendor, the SmartSync feature uses an extended interface between VxVM volumes and
the database software to avoid unnecessary work during mirror resynchronization. For example,
Oracle automatically takes advantage of SmartSync to perform database resynchronization when it
is available.
Volume Sets
Volume sets are an enhancement to VxVM that allow several volumes to be represented by a single
logical mount device. All I/O from and to the underlying volumes is directed via the I/O interfaces
of the volume set. The volume set feature supports the multi-device enhancement to VERITAS File
System (VxFS). This feature allows file systems to make best use of the different performance and
availability characteristics of the underlying volumes. For example, file system metadata could be
stored on volumes with higher redundancy, and user data on volumes with better performance.