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.
fsadm_vxfs(1M) manual pages.