Provided by: amanda-common_3.1.0-1_i386 bug

NAME

       amanda-taperscan - Amanda Taperscan Algorithms

DESCRIPTION

       Amanda uses a taperscan algorithm to select volumes on which to store
       dumps. Historically Amanda has provided only one, fairly complex
       taperscan algorithm, but this algorithm did not suit the needs of all
       users. Now Amanda offers a wide array of algorithms to suit varied
       needs. Adding new algorithms is not difficult.

       The taperscan algorithm is specified with the taperscan parameter,
       which has a default value of traditional.

       Taperscan algorithms are implemented as perl packages with the prefix
       Amanda::Taper::Scan::. See the perl documentation for
       Amanda::Taper::Scan for more information.

TAPERSCAN ALGORITHMS

       In general, these volumes will only select reusable volumes. These are
       volumes which are listed in the tapelist(5) with the reuse flag, and
       which are not among the tapecycle-1 most recent volumes in the list.
       Put another way, reusable volumes do not contain data that must be
       retained. Note that if fewer than tapecycle-1 volumes have been written
       then there are no reusable volumes. Newly labeled volumes (volumes that
       have been labeled with amlabel but never used) are considered reusable.

       Many of these algorithms look for the oldest reusable volume. In most
       cases, this is the best volume to overwrite, as the data it contains is
       older than that on any other volume. If there are no reusable volumes,
       then there is no oldest reusable volume.

   traditional
       This algorithm duplicates Amanda┬┤s historical behavior, and it operates
       in two stages.

       First, if there is an oldest reusable volume and if the changer
       supports "fast" searches, then the algorithm uses the changer to search
       for that volume. Newly labeled volumes are not considered when
       calculating the oldest reusable volume. Consequently, this taperscan
       algorithm prefers volumes which have been used before to newly-labeled
       volumes when a fast-searchable changer is in use.

       Second, if there is no oldest reusable volume, or if that volume is not
       available in the changer, then the algorithm begins a sequential scan
       of the changer, starting at the current slot. It selects the first
       suitable volume it finds: a reusable volume (perhaps newly-labeled) or,
       if label_new_tapes is true, a blank volume. Even across multiple
       invocations (when runtapes > 1), it will not return the same slot
       twice.

           Note
           This algorithm shows an undue preference for volumes already
           containing data, by omitting newly-labeled volumes from its first
           stage.  Historically, many Amanda changer scripts were not
           fast-searchable (including chg-multi, chg-disk and, if
           havereader=0, chg-zd-mtx), and thus skipped the first stage,
           allowing new volumes to find their way into the tape cycle.  New
           changers are almost all fast-searchable, so both stages of the
           algorithm are used and new tapes may be unexpectedly excluded.  If
           this causes an undesirable change in behavior, consider one of the
           other taperscan algorithms..sp .5v

SEE ALSO

       amanda(8), amanda.conf(5), tapelist(5), amanda-changers(7)

       The Amanda Wiki: : http://wiki.zmanda.com/

AUTHOR

       Dustin J. Mitchell <dustin@zmanda.com>
           Zmanda, Inc. (http://www.zmanda.com)