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NAME
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buildindex, checkarenas, checkindex, conf, fmtarenas, fmtbloom,
fmtindex, fmtisect, syncindex – prepare and maintain a venti server
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SYNOPSIS
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venti/fmtarenas [ −4Z ] [ −a arenasize ] [ −b blocksize ] name
file
venti/fmtisect [ −1Z ] [ −b blocksize ] name file
venti/fmtbloom [ −n nblocks | −N nhash ] [ −s size ] file
venti/fmtindex [ −a ] venti.conf
venti/conf [ −w ] partition [ configfile ]
venti/buildindex [ −bd ] [ −i isect ] ... [ −M imemsize ] venti.conf
venti/checkindex [ −f ] [ −B blockcachesize ] venti.conf tmp
venti/checkarenas [ −afv ] file
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DESCRIPTION
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These commands aid in the setup, maintenance, and debugging of
venti servers. See venti(7) for an overview of the venti system
and venti(8) for an overview of the data structures used by the
venti server.
Note that the units for the various sizes in the following commands
can be specified by appending k, m, or g to indicate kilobytes,
megabytes, or gigabytes respectively.
Formatting
To prepare a server for its initial use, the arena partitions
and the index sections must be formatted individually, with fmtarenas
and fmtisect. Then the collection of index sections must be combined
into a venti index with fmtindex.
Fmtarenas formats the given file, typically a disk partition,
into an arena partition. The arenas in the partition are given
names of the form name%d, where %d is replaced with a sequential
number starting at 0.
Options to fmtarenas are:
−a arenasize
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The arenas are of arenasize bytes. The default is 512M, which
was selected to provide a balance between the number of arenas
and the ability to copy an arena to external media such as recordable
CDs and tapes.
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−b blocksize
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The size, in bytes, for read and write operations to the file.
The size is recorded in the file, and is used by applications
that access the arenas. The default is 8k.
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−4 Create a ‘version 4’ arena partition for backwards compatibility
with old servers. The default is version 5, used by the current
venti server.
−Z Do not zero the data sections of the arenas. Using this option
reduces the formatting time but should only be used when it is
known that the file was already zeroed. (Version 4 only; version
5 sections are not and do not need to be zeroed.)
Fmtisect formats the given file, typically a disk partition, as
a venti index section with the specified name. Each of the index
sections in a venti configuration must have a unique name.
Options to fmtisect are:
−b bucketsize
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The size of an index bucket, in bytes. All the index sections
within a index must have the same bucket size. The default is
8k.
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−1 Create a ‘version 1’ index section for backwards compatibility
with old servers. The default is version 2, used by the current
venti server.
−Z Do not zero the index. Using this option reduces the formatting
time but should only be used when it is known that the file was
already zeroed. (Version 1 only; version 2 sections are not and
do not need to be zeroed.)
Fmtbloom formats the given file as a Bloom filter (see venti(7)).
The options are:
−n nblock | −N nhash
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The number of blocks expected to be indexed by the filter or the
number of hash functions to use. If the −n option is given, it
is used, along with the total size of the filter, to compute an
appropriate nhash.
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−s sizeThe size of the Bloom filter. The default is the total
size of the file. In either case, size is rounded down to a power
of two.
The file argument in the commands above can be of the form file:lo−hi
to specify a range of the file. Lo and hi are specified in bytes
but can have the usual k, m, or g suffixes. Either lo or hi may
be omitted. This notation eliminates the need to partition raw
disks on non-Plan 9 systems.
Fmtindex reads the configuration file venti.conf and initializes
the index sections to form a usable index structure. The arena
files and index sections must have previously been formatted using
fmtarenas and fmtisect respectively.
The function of a venti index is to map a SHA1 fingerprint to
a location in the data section of one of the arenas. The index
is composed of blocks, each of which contains the mapping for
a fixed range of possible fingerprint values. Fmtindex determines
the mapping between SHA1 values and the blocks of the collection
of index sections. Once this
mapping has been determined, it cannot be changed without rebuilding
the index. The basic assumption in the current implementation
is that the index structure is sufficiently empty that individual
blocks of the index will rarely overflow. The total size of the
index should be about 2% to 10% of the total size of the arenas,
but the exact percentage
depends both on the index block size and the compressed size of
blocks stored. See the discussion in venti(8) for more.
Fmtindex also computes a mapping between a linear address space
and the data section of the collection of arenas. The −a option
can be used to add additional arenas to an index. To use this
feature, add the new arenas to venti.conf after the existing arenas
and then run fmtindex −a.
A copy of the above mappings is stored in the header for each
of the index sections. These copies enable buildindex to restore
a single index section without rebuilding the entire index.
To make it easier to bootstrap servers, the configuration file
can be stored in otherwise empty space at the beginning of any
venti partitions using conf. A partition so branded with a configuration
file can be used in place of a configuration file when invoking
any of the venti commands. By default, conf prints the configuration
stored in partition. When
invoked with the −w flag, conf reads a configuration file from
configfile (or else standard input) and stores it in partition.
Checking and Rebuilding
Buildindex populates the index for the Venti system described
in venti.conf. The index must have previously been formatted using
fmtindex. This command is typically used to build a new index
for a Venti system when the old index becomes too small, or to
rebuild an index after media failure. Small errors in an index
can usually be fixed with
checkindex, but checkindex requires a large temporary workspace
and buildindex does not.
Options to buildindex are:
−b Reinitialise the Bloom filter, if any.
−d ‘Dumb’ mode; run all three passes.
−i isect Only rebuild index section isect; may be repeated to rebuild
multiple sections. The name none is special and just reads the
arenas.
−M imemsizeThe amount of memory, in bytes, to use for caching
raw disk accesses while running buildindex. (This is not a property
of the created index.) The usual suffices apply. The default is
256M.
Checkindex examines the Venti index described in venti.conf. The
program detects various error conditions including: blocks that
are not indexed, index entries for blocks that do not exist, and
duplicate index entries. If requested, an attempt can be made
to fix errors that are found.
The tmp file, usually a disk partition, must be large enough to
store a copy of the index. This temporary space is used to perform
a merge sort of index entries generated by reading the arenas.
Options to checkindex are:
−B blockcachesize
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The amount of memory, in bytes, to use for caching raw disk accesses
while running checkindex. The default is 8k.
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−f Attempt to fix any errors that are found.
Checkarenas examines the Venti arenas contained in the given file.
The program detects various error conditions, and optionally attempts
to fix any errors that are found.
Options to checkarenas are:
−a For each arena, scan the entire data section. If this option
is omitted, only the end section of the arena is examined.
−f Attempt to fix any errors that are found.
−v Increase the verbosity of output.
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SOURCE
SEE ALSO
BUGS
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Buildindex should allow an individual index section to be rebuilt.
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