venti-fmt man page on Plan9

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VENTI-FMT(8)							  VENTI-FMT(8)

       buildindex,  checkarenas, checkindex, conf, fmtarenas, fmtbloom, fmtin‐
       dex, fmtisect - prepare and maintain a venti server

       venti/fmtarenas [ -Z ] [ -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

       These commands aid in the setup, maintenance, and  debugging  of	 venti
       servers.	 See venti(6) 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 or to indicate kilobytes, megabytes, or giga‐
       bytes respectively.

       To prepare a server for its initial use, the arena partitions  and  the
       index sections must be formatted individually, with fmtarenas and fmti‐
       sect.  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

       Options to fmtarenas are:

       -a arenasize
	      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.

       -b blocksize
	      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.

       -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; ver‐
	      sion 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
	      The size of an index bucket, in bytes.  All the  index  sections
	      within  a	 index must have the same bucket size.	The default is

       -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(6)).  The
       options are:

       -n nblock | -N nhash
	      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.

       -s size
	      The  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

       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 omit‐
       ted.  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	 loca‐
       tion  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 pos‐
       sible 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 percent‐
       age 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  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	parti‐
       tions 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 parti‐
       tion.  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 fmtin‐
       dex.   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 is special and just reads the  are‐

       -M imemsize
	      The  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

       Checkindex examines the Venti index described in venti.conf.  The  pro‐
       gram  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
	      The amount of memory, in bytes, to  use  for  caching  raw  disk
	      accesses while running checkindex.  The default is 8k.

       -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.


       venti(6), venti(8)

       Buildindex should allow an individual index section to be rebuilt.

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