Veritas File System (VxFS) provides API functions frequently associated with commercial applications that make it possible to perform the following actions:
Preallocate space for a file
Specify a fixed extent size for a file
Bypass the system buffer cache for file I/O
Specify the expected access pattern for a file
Because these functions are provided using VxFS-specific IOCTL system calls, most existing UNIX system applications do not use them. For portability reasons, these applications must check which file system type they are using before using these functions.