cachefs(4)

NAME
     cachefs - Cache File System Description

DESCRIPTION
     Cachefs is a file system layered above other standard IRIX file systems.
     It performs automatic local caching of data from one file system (called
     the back file system) on another file system (called the front file
     system).  Any the following file systems may be used as the front file
     system:  xfs and efs.  Any of the following file systems may be used as
     the back file system:  nfs, nfs3, iso9660, cdfs, hfs, kfs, and dos.

     Data from the back file system is cached on the front file system when it
     is first accessed.  Subsequent accesses will retrieve the data from the
     front file system.  Consistency will be maintained with the back file
     system in a manner similar to that used for NFS.

TERMINOLOGY
     front file system
          This is the local file system on which data is cached.  The
          supported back file system types are xfs and efs.

     back file system
          This is the file system which contains the definitive copy of the
          data.  Data is retrieved from this file system and cached on the
          front file system.  Refer to fstab(4) for a list of supported back
          file system types.

     cnode
          This is the internal data structure used by cachefs to manage its
          files.  There is one cnode for each open file.  Each cnode occupies
          128 bytes on a 32 bit system and 256 bytes on a 64 bit system.  In
          addition, each cnode points to a dynamically allocated area of 512
          bytes containing metadata and attributes.

TUNING
     Cachefs has a number of different tuning parameters, some of which are
     supplied on the mount(1M) command (see fstab(4)), some of which are
     supplied via cfsadmin(1M), and some of which are kernel tuanbles
     adjustable with systune(1M).

     The kernel tunables are adjustable on a running kernel and control
     readahead, asynchronous operations, and cnode caching.  The kernel
     tunables are described below.

       cachefs_readahead
            This controls the number of blocks to read ahead of the current
            block being read.  These will be read asynchronously.  The size of
            a block is whatever the preferred I/O size is for the front file
            system.
       cachefs_max_threads
            This is the maximum number of asynchronous I/O daemons allowed to
            be running per cachefs mounted file system.

       fileheader_cache_size
            This is the size in 512-byte units of the in-memory cache of file
            header information (cached attributes and other metadata).  This
            number indicates the number of such headers retained after other
            system internal data (e.g., the vnode) for a file has been
            released.

SEE ALSO
     cfsadmin(1M), fstab(4), systune(1M)