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AMANDA-TAPERSCAN(7)		  Miscellanea		   AMANDA-TAPERSCAN(7)

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)

Amanda 3.3.9			  02/09/2016		   AMANDA-TAPERSCAN(7)

NAME | DESCRIPTION | DEFINING A TAPERSCAN | TAPERSCAN ALGORITHMS | SEE ALSO | AUTHOR

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