NAME

mkvffs − create a VF file system

SYNOPSIS

/etc/vf/mkvffs special blocks inodes primary secondary [fsname volume]

DESCRIPTION

mkvffs creates a file system of type Very Fast (VF) by writing into the file special. The VF file system is designed for the high-speed sequential reading and writing of large files.  The remaining arguments of the command line define the parameters of the file system:

blocks specifies the size of the entire file system in 512-byte blocks. 

inodes specifies the number of inodes. 

primary specifies the default primary extent size in 1K logical blocks. 

secondary specifies the default secondary extent size in 1K logical blocks. 

fsname and volume specify optional file system and volume names, which are limited to six characters each. 

Note that mkvffs is in /etc/vf, which is not in the standard root (superuser) PATH.  It can be linked into /etc for easier access. 

Extent Sizes

An extent is a set of contiguous 1K data blocks in a VF file system.  When a file is first written, an initial primary extent is allocated.  After all the blocks in the primary extent have been written, additional secondary extents are allocated as needed.  To minimize file discontinuities, a new secondary extent is allocated contiguous to the preceding extent whenever possible. 

When a VF file system is created, it is given default primary and secondary extent size attributes.  A file inherits these default extent size attributes when it is created.  The extent sizes of a file can be changed with an fcntl(2) system call command as described in vf(4), which allows a program that knows the size of the file it will write to specify a primary extent size that can contain the entire file.

The default primary and secondary extent sizes should be chosen carefully based upon the sizes of the files that will be stored in the file system.  If the primary extent size is much larger than the files, a great deal of space will be wasted.  If the primary and secondary extent sizes are much smaller than the files, files may be fragmented, resulting in less efficient data transfers, and attempts to write files may fail because the limit of 12 non-contiguous extents per file is exceeded. 

SEE ALSO

fcntl(2), vf(4) in the INTERACTIVE SDS Guide and Programmer’s ­Reference Manual. The “Very Fast File System (VF)” section in the “INTERACTIVE UNIX Operating System Maintenance Procedures” in the INTERACTIVE UNIX Operating System Guide.

ADDED VALUE

This entry, supplied by Sun Microsystems, Inc., is an extension of UNIX System V. 

\*U  —  Version 1.0