Veritas™ File System 5.0.1 Administrator's Guide

You can then configure policies that automatically relocate files from one volume
to another, or relocate files by running file relocation commands. Having multiple
volumes lets you determine where files are located, which can improve
performance for applications that access specific types of files. DST functionality
is a separately licensed feature and is available with the VRTSfppm package.
See “About Dynamic Storage Tiering” on page 143.
Thin Reclamation of a file system
Storage is allocated from a Thin Storage LUN when files are created and written
to a file system. This storage is not given back to the Thin Storage LUN when a
file is deleted or the file size is shrunk. As such, the file system must perform the
explicit task of releasing the free storage to the Thin Storage LUN. This is
performed by the Storage Foundation Thin Reclamation feature. Thin Reclamation
is only supported on VxFS file systems mounted on a VxVM volume.
Veritas File System performance enhancements
Traditional file systems employ block-based allocation schemes that provide
adequate random access and latency for small files, but which limit throughput
for larger files. As a result, they are less than optimal for commercial
environments.
VxFS addresses this file system performance issue through an alternative
allocation method and increased user control over allocation, I/O, and caching
policies.
See “Using Veritas File System” on page 29.
VxFS provides the following performance enhancements:
■ Data synchronous I/O
■ Direct I/O and discovered direct I/O
■ Support for files and file systems up to 256 terabytes
■ Support for files up to 2 terabytes
■ Enhanced I/O performance
■ Caching advisories
■ Enhanced directory features
■ Explicit file alignment, extent size, and preallocation controls
■ Tunable I/O parameters
27Introducing Veritas File System
Veritas File System performance enhancements