2 .\" Title: amanda-taperscan
3 .\" Author: Dustin J. Mitchell <dustin@zmanda.com>
4 .\" Generator: DocBook XSL Stylesheets vsnapshot_8273 <http://docbook.sf.net/>
6 .\" Manual: Miscellanea
7 .\" Source: Amanda 3.2.1
10 .TH "AMANDA\-TAPERSCAN" "7" "12/14/2010" "Amanda 3\&.2\&.1" "Miscellanea"
11 .\" -----------------------------------------------------------------
12 .\" * set default formatting
13 .\" -----------------------------------------------------------------
14 .\" disable hyphenation
16 .\" disable justification (adjust text to left margin only)
18 .\" -----------------------------------------------------------------
19 .\" * MAIN CONTENT STARTS HERE *
20 .\" -----------------------------------------------------------------
22 amanda-taperscan \- Amanda Taperscan Algorithms
26 \fItaperscan algorithm\fR
27 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\&.
29 The taperscan algorithm is specified with the
31 parameter, which has a default value of
34 Taperscan algorithms are implemented as perl packages with the prefix
35 Amanda::Taper::Scan::\&. See the perl documentation for
37 for more information\&.
38 .SH "TAPERSCAN ALGORITHMS"
40 In general, these volumes will only select reusable volumes\&. These are volumes which are listed in the
44 flag, and which are not among the
46 most recent volumes in the list\&. Put another way, reusable volumes do not contain data that must be retained\&. Note that if fewer than
48 volumes have been written then there are no reusable volumes\&. Newly labeled volumes (volumes that have been labeled with
50 but never used) are considered reusable\&.
52 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\&.
55 This algorithm duplicates Amanda\'s historical behavior, and it operates in two stages\&.
57 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\&.
59 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
62 \fBempty\fR, a blank volume\&. Even across multiple invocations (when
63 \fIruntapes > 1\fR), it will not return the same slot twice\&.
69 .nr an-no-space-flag 1
76 This algorithm shows an undue preference for volumes already containing
77 data, by omitting newly\-labeled volumes from its first stage\&. Historically,
78 many Amanda changer scripts were not fast\-searchable (including
79 \fIchg\-multi\fR, \fIchg\-disk\fR and, if
80 \fIhavereader=0\fR, \fIchg\-zd\-mtx\fR), and thus
81 skipped the first stage, allowing new volumes to find their way into the tape
82 cycle\&. New changers are almost all fast\-searchable, so both stages of the
83 algorithm are used and new tapes may be unexpectedly excluded\&. If this causes
84 an undesirable change in behavior, consider one of the other taperscan
92 \fBamanda-changers\fR(7)
95 : http://wiki.zmanda.com/
98 \fBDustin J\&. Mitchell\fR <\&dustin@zmanda\&.com\&>
100 Zmanda, Inc\&. (http://www\&.zmanda\&.com)