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NAME
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vac – create a vac archive on Venti
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SYNOPSIS
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vac [ −mqsv ] [ −b blocksize ] [ −d oldvacfile ] [ −e exclude
] [ −f vacfile ] [ −i name ] [ −h host ] file ...
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DESCRIPTION
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Vac creates an archival copy of Plan 9 file trees on Venti. It
can be used to build a simple backup system. One of the unusual
properties of Venti is that duplicate blocks are detected and
coalesced. When vac is used on a file tree that shares data with
an existing archive, the consumption of storage will be approximately
equal to an incremental backup. This reduction in storage consumption
occurs transparently to the user.
As an optimization, the −d and −q options, described below, can
be used to explicitly create an archive relative to an existing
archive. These options do not change the resulting archive generated
by vac, but simply reduce the number of write operations to Venti.
The output of vac is the hexadecimal representation of the Sha1
fingerprint of the root of the archive, in this format:
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vac:64daefaecc4df4b5cb48a368b361ef56012a4f46
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Option to vac are:
−b blocksize
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Specifies the block size that data will be broken into. The units
for the size can be specified by appending k to indicate kilobytes.
The default is 8k. The size must be in the range of 512 bytes
to 52k.
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−d oldvacfile
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Reduce the number of blocks written to Venti by comparing the
files to be stored with the contents of an existing vac file tree
given by oldvacfile.
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−e exclude
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Do not include the file or directory specified by exclude. This
option may be repeated multiple times.
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−f vacfile
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The results of vac are place in vacfile, or the standard output
if no file is given.
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−i name
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Include standard input as one of the input files, storing it in
the archive with the specified name.
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−h host
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The network address of the Venti server. The default is taken
from the environment variable venti.
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−m Expand and merge any vac archives that are found while reading
the input files. This option is useful for building an archive
from a collection of existing archives. Each archive is inserted
into the new archive as if it had been unpacked in the directory
in which it was found. Multiple archives can be unpacked in
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a single directory and the contents will be merged. To be detected,
the archives must end in .vac. Note, an archive is inserted by
simply copying the root fingerprint and does not require the archive
to be unpacked.
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−q Increase the performance of the −d option by detecting unchanged
files based on a match of the files name and other meta data,
rather than examining the contents of the files.
−s Print out various statistics on standard error.
−v Produce more verbose output on standard error, including the
name of the files added to the archive and the vac archives that
are expanded and merged.
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SOURCE
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/usr/local/plan9/src/cmd/vac
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SEE ALSO
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Plan 9’s vacfs(4) and venti(8)
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