Veritas File System 5.1 SP1 Administrator"s Guide (5900-1499, April 2011)

Partitioned directories

Normally, a large volume of parallel threads performing access and updates on a

directory that commonly exist in an file system suffers from exponentially longer

wait times for the threads. This feature creates partitioned directories to improve

the directory performance of file systems. When any directory crosses the tunable

threshold, this feature takes an exclusive lock on the directory inode and

redistributes the entries into various respective hash directories. These hash

directories are not visible in the name-space view of the user or operating system.

For every new create, delete, or lookup thread, this feature performs a lookup for

the respective hashed directory (depending on the target name) and performs the

operation in that directory. This leaves the parent directory inode and its other

hash directories unobstructed for access, which vastly improves file system

performance.

This feature operates only on disk layout Version 8 or later file systems.

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 30.

VxFS provides the following performance enhancements:

■ Data synchronous I/O

■ Direct I/O and discovered direct I/O

■ Support for file systems up to 256 terabytes

■ Support for files up to 16 terabytes

■ Enhanced I/O performance

■ Caching advisories

■ Enhanced directory features

■ Explicit file alignment, extent size, and preallocation controls

■ Tunable I/O parameters

■ Tunable indirect data extent size

Introducing Veritas File System

Veritas File System performance enhancements