AMANDA-TAPERSCAN(7) Miscellanea AMANDA-TAPERSCAN(7)NAMEamanda-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 ALSOamanda(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 3.3.3 01/10/2013 AMANDA-TAPERSCAN(7)