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| The '''Taper scan algorithm''' is the algorithm used to determine which volume, if any, is the next to be written by [[taper]]. The policy is as follows:
| | See {{man|7|amanda-taperscan}}. |
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| Consider the set of tapes ''T''. We can partition the set into two disjoint
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| subsets ''A'' (the set of active tapes) and ''I'' (the set of inactive tapes).
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| Assuming I is nonempty, there exists a subset ''P'' of ''I'', called the set of
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| preferred tapes. Note that ''T'' = ''A'' + ''I'', ''P'' ⊆ ''I'', and ''A'' ∩ ''I'' = ∅.
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| Amanda will only use tapes from ''I''; active tapes are not considered for
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| overwriting. Also, tapes from ''P'' are preferred to other tapes in ''I''; a tape not
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| in ''P'' (but in ''I'') will be used only if no tapes in ''P'' are available. If no tapes
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| from ''I'' are available, then no tapes are used and Amanda will go into degraded
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| mode.
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| Tapes are assigned to each of the sets as follows:
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| * Any labeled but unused tapes are in both ''I'' and ''P''. This includes unlabeled tapes if the label_new_tapes option is set.
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| * The most recently used "tapecycle" - 1 number of tapes is in ''A''.
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| * Any remaining tapes are in ''I''. The single least recently used of these is also in ''P''.
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| This algorithm is applied from scratch any time a new tape is needed during a
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| backup run. You can run the algorithm without running Amanda by doing 'amtape
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| taper'.
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| ==== Other uses of tapecycle ====
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| The <tt>tapecycle</tt> configuration parameter, in addition to the usage above, is used by the <tt>chg-disk</tt> changer driver to determine the number of virtual slots. When setting <tt>tapecycle</tt> to something other than the total number of slots in the virtual changer, create a separate configuration for for chg-disk, and specify <tt>LASTSLOT=''n''</tt>, where ''n'' is the actual number of virtual slots.
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