Veritas File System (VxFS) allocates disk space to files in groups of one or more adjacent blocks called extents. VxFS defines an application interface that allows programs to control various aspects of the extent allocation for a given file. The extent allocation policies associated with a file are referred to as extent attributes.
The VxFS getext and setext commands let you view or manipulate file extent attributes.
getext(1) manual pages.
The two basic extent attributes associated with a file are its reservation and its fixed extent size. You can preallocate space to the file by manipulating a file's reservation, or override the default allocation policy of the file system by setting a fixed extent size.
See Fixed extent size.
You can specify the following criteria:
The space reserved for a file must be contiguous
No allocations will be made for a file beyond the current reservation
An unused reservation will be released when the file is closed
Space will be allocated, but no reservation will be assigned
The file size will be changed to incorporate the allocated space immediately
Some of the extent attributes are persistent and become part of the on-disk information about the file, while other attributes are temporary and are lost after the file is closed or the system is rebooted. The persistent attributes are similar to the file's permissions and are written in the inode for the file. When a file is copied, moved, or archived, only the persistent attributes of the source file are preserved in the new file.