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.

DEFINING A TAPERSCAN

       An taperscan is defined in amanda.conf(5) as follows:

       define taperscan $taperscan_name {
          comment "$comment"
          plugin "$pluginname"
          property "$PROPERTY_NAME" "$PROPERTY_VALUE"
          ...
       }
       and then referenced in the global section as

         taperscan "$taperscan_name"

       Taperscan properties, like Amanda configuration parameters, are insensitive to case, and -
       (dash) and _ (underscore) may be used interchangeably.

       See the individual plugin documentation below for properties applicable to each plugin.

TAPERSCAN ALGORITHMS

       In general, these algorithms 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 autolabel includes empty, 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

   oldest
       This algorithm works with the Changer API (see amanda-changers(7)), using the inventory
       returned by the changer to locate the oldest acceptable volume available. Note that this
       will not work with changers that do not support inventory (old changers). The algorithms
       scans unknown slots only if no known usable volume is found in the inventory.

       An acceptable volume is a reusable volume, a new labeled volume or an unlabeled volume
       that can be labeled according to autolabel. Note that changers do not always know the
       contents of every slot - for example, a tape with an unknown barcode will not be
       considered usable.

       Use amtape CONF inventory to see the changer's inventory, and use amtape CONF update to
       update it.

   lexical
       This algorithm also works with the Changer API, using the inventory to determine the
       acceptable volumes; it then uses the volume which follows the last-used volume in lexical
       order. For volume labels containing leading zeros, e.g., CORP-010, this algorithm will run
       through the volumes in the natural order.

       It scans unknown slots only if no usable volume is found in the inventory.

       See oldest, above, for a definition of acceptable volumes.

SEE ALSO

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

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

AUTHOR

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