Veritas Storage Foundation™ for Oracle 5.0.1 Administrator's Guide

If you are restoring some of the files in the file system, you should first remove
the data-full Storage Checkpoints that are no longer needed. If you have very
limited free space on the file system, you may have to remove all data-full Storage
Checkpoints in order for the restore to succeed.
Always reserve free disk space for growing volumes and file systems. You can also
preallocate sufficient space for each file system when the file system is first created
or manually grow the file system and logical volume where the file system resides.
See the vxassist(1) and fsadm_vxfs(1) manual pages for more information.
Performance of Storage Checkpoints
Veritas File System attempts to optimize the read and write access performance
on both the Storage Checkpoint and the primary file system. Reads from a Storage
Checkpoint typically perform at nearly the throughput of reads from a normal
VxFS file system, allowing backups to proceed at the full speed of the VxFS file
system.
Writes to the primary file system are typically affected by the Storage Checkpoints
because the initial write to a data block requires a read of the old data, a write of
the data to the Storage Checkpoint, and finally, the write of the new data to the
primary file system. Having multiple Storage Checkpoints on the same file system,
however, will not make writes slower. Only the initial write to a block suffers this
penalty, allowing operations like writes to the intent log or inode updates to
proceed at normal speed after the initial write.
The performance impact of Storage Checkpoints on a database is less when the
database files are Direct I/O files. A performance degradation of less than 5% in
throughput has been observed in a typical OLTP workload when the Storage
Checkpoints only keep track of changed information. For Storage Checkpoints
that are used for Storage Rollback, higher performance degradation (approximately
10 to 20 percent) has been observed in an OLTP workload. The degradation should
be lower in most decision-support or data warehousing environments.
Reads from the Storage Checkpoint are impacted if the primary file system is
busy, because the reads on the Storage Checkpoint are slowed by all of the disk
I/O associated with the primary file system. Therefore, performing database
backup when the database is less active is recommended.
Storage Checkpoint allocation policies
The Veritas File System provides Multi-Volume File Systems (MVS) when used in
conjunction with the Volumes Set feature in Veritas Volume Manager. A volume
set is a container for multiple different volumes. MVS enables creation of a single
153Using Storage Checkpoints and Storage Rollback
Performance of Storage Checkpoints