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cachefs(4)							    cachefs(4)

NAME    [Toc]    [Back]

     cachefs - Cache File System Description

DESCRIPTION    [Toc]    [Back]

     Cachefs is	a file system layered above other standard IRIX	file systems.
     It	performs automatic local caching of data from one file system
     (typically	remote)	on a local file	system.	 Any of	the following file
     systems may be used for the cached	data:  xfs and efs.  Any of the
     following file systems may	be used	as the source of data to be cached:
     nfs, nfs3,	iso9660, cdfs, hfs, kfs, and dos.

     Data is cached when it is first accessed.	Subsequent accesses will
     retrieve the data from the	cache.	Consistency will be maintained in a
     manner similar to that used for NFS.

TERMINOLOGY    [Toc]    [Back]

     front file	system
	  This is the local file system	on which cached	data is	stored.

     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.

	  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    [Toc]    [Back]

     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.

	    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

	    This is the	maximum	number of asynchronous I/O daemons allowed to
	    be running per cachefs mounted file	system.

									Page 1

cachefs(4)							    cachefs(4)

	    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

	    This controls the time between reconstructions of the replacement
	    list by the	replacement daemon (cachefs_replacement).  If no
	    replacement	requests are made by the kernel	within this time
	    limit, the daemon will time	out and	reconstruct the	list.


     Mounts of cachefs file systems performed at system	startup	use options
     supplied in /etc/config/cachefs.options. This file	may contain any
     options for mount(1M) desired.  Of	particular interest is the "-m"
     option.  This option allows the administrator to limit the	number of
     parallel mount processes mounting cachefs file systems.  This will	be
     required on systems where some cachefs file systems fail to mount due to
     a lack of swap space.

LIMITATIONS    [Toc]    [Back]

     Mandatory file locking is not supported on	cachefs.

SEE ALSO    [Toc]    [Back]

     cfsadmin(1M), fstab(4), systune(1M), mount(1M)

									PPPPaaaaggggeeee 2222
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