Veritas Storage Foundation™ for Oracle 5.0.1 Administrator's Guide

About extent-based allocation
The HFS file system supplied with HP-UX uses block-based allocation schemes
that provide good random access to files and acceptable latency on small files.
For larger files, like database files, this block-based architecture limits throughput.
This limitation makes the HFS file system a less than optimal choice for database
environments.
When storage is allocated to a file on a VxFS file system, it is grouped in extents,
as opposed to being allocated a block at a time as with the HFS file system.
By allocating disk space to files in extents, disk I/O to and from a file can be done
in units of multiple blocks. This type of I/O can occur if storage is allocated in
units of consecutive blocks. For sequential I/O, multiple block operations are
considerably faster than block-at-a-time operations. Almost all disk drives accept
I/O operations of multiple blocks.
The VxFS file system allocates disk space to files in groups of one or more extents.
VxFS also allows applications to control some aspects of the extent allocation for
a given file. Extent attributes are the extent allocation policies associated with a
file.
See “Preallocating space for Quick I/O files using the setext command” on page 82.
About fast file system and database recovery
Veritas File System begins recovery procedures within seconds after a system
failure by using a tracking feature called intent logging. This feature records
pending changes to the file system structure in a circular intent log. The intent
log recovery feature is not readily apparent to users or a system administrator
except during a system failure. During system failure recovery, the VxFS fsck
utility performs an intent log replay, which scans the intent log and nullifies or
completes file system operations that were active when the system failed. The
file system can then be mounted without completing a full structural check of the
entire file system. Replaying the intent log may not completely recover the
damaged file system structure if there was a disk hardware failure; hardware
problems may require a complete system check using the fsck utility provided
with Veritas File System.
About online system administration
The VxFS file system provides online system administration utilities to help
resolve certain problems that impact database performance. You can defragment
and resize a VxFS file system while it remains online and accessible to users.
33Introducing Veritas Storage Foundation for Oracle
How Veritas File System works