1AMANDA-TAPERSCAN(7) Miscellanea AMANDA-TAPERSCAN(7)
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6 amanda-taperscan - Amanda Taperscan Algorithms
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9 Amanda uses a taperscan algorithm to select volumes on which to store
10 dumps. Historically Amanda has provided only one, fairly complex
11 taperscan algorithm, but this algorithm did not suit the needs of all
12 users. Now Amanda offers a wide array of algorithms to suit varied
13 needs. Adding new algorithms is not difficult.
14 The taperscan algorithm is specified with the taperscan parameter,
16 which has a default value of traditional.
17 Taperscan algorithms are implemented as perl packages with the prefix
19 Amanda::Taper::Scan::. See the perl documentation for
20 Amanda::Taper::Scan for more information.
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23 An taperscan is defined in amanda.conf(5) as follows:
24 define taperscan $taperscan_name {
26 comment "$comment"
27 plugin "$pluginname"
28 property "$PROPERTY_NAME" "$PROPERTY_VALUE"
29 ...
30 }
31 and then referenced in the global section as
32 taperscan "$taperscan_name"
34 Taperscan properties, like Amanda configuration parameters, are
36 insensitive to case, and - (dash) and _ (underscore) may be used
37 interchangeably.
38 See the individual plugin documentation below for properties applicable
40 to each plugin.
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43 In general, these algorithms will only select reusable volumes. These
44 are volumes which are listed in the tapelist(5) with the reuse flag,
45 and which are not among the tapecycle-1 most recent volumes in the
46 list. Put another way, reusable volumes do not contain data that must
47 be retained. Note that if fewer than tapecycle-1 volumes have been
48 written then there are no reusable volumes. Newly labeled volumes
49 (volumes that have been labeled with amlabel but never used) are
50 considered reusable.
51 Many of these algorithms look for the oldest reusable volume. In most
53 cases, this is the best volume to overwrite, as the data it contains is
54 older than that on any other volume. If there are no reusable volumes,
55 then there is no oldest reusable volume.
56 traditional
58 This algorithm duplicates Amanda's historical behavior, and it operates
59 in two stages.
60 First, if there is an oldest reusable volume and if the changer
62 supports "fast" searches, then the algorithm uses the changer to search
63 for that volume. Newly labeled volumes are not considered when
64 calculating the oldest reusable volume. Consequently, this taperscan
65 algorithm prefers volumes which have been used before to newly-labeled
66 volumes when a fast-searchable changer is in use.
67 Second, if there is no oldest reusable volume, or if that volume is not
69 available in the changer, then the algorithm begins a sequential scan
70 of the changer, starting at the current slot. It selects the first
71 suitable volume it finds: a reusable volume (perhaps newly-labeled) or,
72 if autolabel includes empty, a blank volume. Even across multiple
73 invocations (when runtapes > 1), it will not return the same slot
74 twice.
75 Note
77 This algorithm shows an undue preference for volumes already
78 containing data, by omitting newly-labeled volumes from its first
79 stage. Historically, many Amanda changer scripts were not
80 fast-searchable (including chg-multi, chg-disk and, if
81 havereader=0, chg-zd-mtx), and thus skipped the first stage,
82 allowing new volumes to find their way into the tape cycle. New
83 changers are almost all fast-searchable, so both stages of the
84 algorithm are used and new tapes may be unexpectedly excluded. If
85 this causes an undesirable change in behavior, consider one of the
86 other taperscan algorithms..sp .5v
87 oldest
89 This algorithm works with the Changer API (see amanda-changers(7)),
90 using the inventory returned by the changer to locate the oldest
91 acceptable volume available. Note that this will not work with changers
92 that do not support inventory (old changers). The algorithms scans
93 unknown slots only if no known usable volume is found in the inventory.
94 An acceptable volume is a reusable volume, a new labeled volume or an
96 unlabeled volume that can be labeled according to autolabel. Note that
97 changers do not always know the contents of every slot - for example, a
98 tape with an unknown barcode will not be considered usable.
99 Use amtape CONF inventory to see the changer's inventory, and use
101 amtape CONF update to update it.
102 lexical
104 This algorithm also works with the Changer API, using the inventory to
105 determine the acceptable volumes; it then uses the volume which follows
106 the last-used volume in lexical order. For volume labels containing
107 leading zeros, e.g., CORP-010, this algorithm will run through the
108 volumes in the natural order.
109 It scans unknown slots only if no usable volume is found in the
111 inventory.
112 See oldest, above, for a definition of acceptable volumes.
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116 amanda(8), amanda.conf(5), tapelist(5), amanda-changers(7), amanda-
117 interactivity(7)
118 The Amanda Wiki: : http://wiki.zmanda.com/
120
122 Dustin J. Mitchell <dustin@zmanda.com>
123 Zmanda, Inc. (http://www.zmanda.com)
124Amanda 3.5.1 12/01/2017 AMANDA-TAPERSCAN(7)