Ubuntu Feisty 7.04 manual page repository

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Provided by: openafs-client_1.4.4-1_i386



        afs_cache - Format of data stored in an AFS client disk cache


        The disk cache on a client machine is composed of multiple Vn files
        that contain the data, a CacheItems file that records index information
        for all of the Vn files, and a VolumeItems file that records the map‐
        ping between volume name and mount point for volumes.
        When it initializes, the Cache Manager creates the cache files in the
        configured cache location.  The standard directory name is
        /usr/vice/cache, but it is acceptable to use a directory on a partition
        with more available space. To designate a different directory, change
        the value in the second field of the /etc/openafs/cacheinfo file before
        issuing the afsd command, or include the -cachedir argument to the afsd
        The CacheItems file records information about each file in the disk
        cache on a client machine (each Vn file). The information includes the
        file ID number and associated volume version number of the AFS file
        currently stored in the Vn file, which enables the Cache Manager to
        determine which Vn file contains the AFS data it needs to present to an
        As it initializes, the Cache Manager creates the binary-format CacheIt‐
        ems file in the same local disk cache directory as the Vn files that
        the CacheItems file describes, and it must always remain there.
        The VolumeItems file records the mapping between volume name and mount
        point for each volume that the Cache Manager has accessed since it ini‐
        tialized on a client machine using a disk cache. The Cache Manager uses
        the mappings to respond correctly to queries about the current working
        directory, which can come from the operating system or commands such as
        the UNIX pwd command.
        As it initializes, the Cache Manager creates the binary-format Vol‐
        umeItems file in the local disk cache directory, and it must always
        remain there.
        A Vn file can store a chunk of cached AFS data on a client machine that
        is using a disk cache. As the Cache Manager initializes, it verifies
        that the local disk cache directory houses a number of Vn files equal
        to the largest of the following:
        ·   100
        ·   One and a half times the result of dividing the cache size by the
            chunk size (cachesize/chunksize * 1.5).
        ·   The result of dividing the cache size by 10 MB (10,240).
        The Cache Manager determines the cache size from the -blocks argument
        to the afsd command, or if the argument is not included, from the third
        field of the /etc/openafs/cacheinfo file.  The default chunk size is 64
        KB; use the -chunksize argument to the afsd command to override it. To
        override the default number of chunks resulting from the calculation,
afsd(8) describes the
        restrictions on acceptable values for each of the arguments.
        If the disk cache directory houses fewer Vn files than necessary, the
        Cache Manager creates new ones, assigning each a unique integer n that
        distinguishes it from the other files; the integers start with 1 and
        increment by one for each Vn file created. The Cache Manager removes
        files if there are more than necessary. The Cache Manager also adds and
        removes Vn files in response to the fs setcachesize command, which can
        be used to alter the cache size between reboots.
        Vn files expand and contract to accommodate the size of the AFS direc‐
        tory listing or file they temporarily house. As mentioned, by default
        each Vn file holds up to 64 KB (65,536 bytes) of a cached AFS element.
        AFS elements larger than 64 KB are divided among multiple Vn files. If
        an element is smaller than 64 KB, the Vn file expands only to the
        required size. A Vn file accommodates only a single element, so if
        there many small cached elements, it is possible to exhaust the avail‐
        able Vn files without reaching the maximum cache size.


        Editing or removing the CacheItems or VolumeItems files or a Vn file
        can cause a kernel panic. If the contents of Vn files seem out of date,
        clear the files by using the fs flush or fs flushvolume command. If any
        of the cache files are accidentally modified or deleted, rebooting the
        machine usually restores normal performance.
        To alter cache size (and thus the number of Vn files) between reboots,
        use the fs setcachesize command. Alternatively, alter the value of the
        -blocks, -files or -chunksize arguments to the afsd command invoked in
        the machine’s AFS initialization file, and reboot. To refresh the con‐
        tents of one or more Vn files, use the fs flush or fs flushvolume com‐
fs_flush(1), fs_flushvol‐


        IBM Corporation 2000. <http://www.ibm.com/> All Rights Reserved.
        This documentation is covered by the IBM Public License Version 1.0.
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        and Russ Allbery, based on work by Alf Wachsmann and Elizabeth Cassell.


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