man/man8/venti-backup.8

.TH VENTI-BACKUP 8
.SH NAME
rdarena, wrarena \- copy arenas between venti servers
.SH SYNOPSIS
.PP
.B venti/rdarena
[
.B -qv
]
.I arenapart
.I arenaname
.PP
.B venti/wrarena
[
.B -o
.I fileoffset
]
[
.B -h
.I host
]
.I arenafile
[
.I clumpoffset
]
.SH DESCRIPTION
.PP
.I Rdarena
extracts the named
.I arena
from the arena partition
.I arenapart
and writes this arena to standard output.
This command is typically used to back up an arena to external media.
The
.B -v
option generates more verbose output on standard error;
.B -q
generates only errors on standard error.
.PP
.I Wrarena
writes the blocks contained in the arena
.I arenafile
(typically, the output of
.IR rdarena )
to a Venti server.
It is typically used to reinitialize a Venti server from backups of the arenas.
For example,
.IP
.EX
venti/rdarena /dev/sdC0/arenas arena.0 >external.media
venti/wrarena -h venti2 external.media
.EE
.LP
writes the blocks contained in
.B arena.0
to the Venti server
.B venti2
(typically not the one using
.BR /dev/sdC0/arenas ).
.PP
The
.B -o
option specifies that the arena starts at byte
.I fileoffset
(default
.BR 0 )
in
.I arenafile .
This is useful for reading directly from
the Venti arena partition:
.IP
.EX
venti/wrarena -h venti2 -o 335872 /dev/sdC0/arenas
.EE
.LP
(In this example, 335872 is the offset shown in the Venti
server's index list (344064) minus one block (8192).
You will need to substitute your own arena offsets
and block size.)
.PP
Finally, the optional
.I offset
argument specifies that the writing should begin with the
clump starting at
.I offset
within the arena.
.I Wrarena
prints the offset it stopped at (because there were no more data blocks).
This could be used to incrementally back up a Venti server
to another Venti server:
.IP
.EX
last=`{cat last}
venti/wrarena -h venti2 -o 335872 /dev/sdC0/arenas $last >output
awk '/^end offset/ { print $3 }' offset >last
.EE
.LP
Of course, one would need to add wrapper code to keep track
of which arenas have been processed.
See
.B /sys/src/cmd/venti/words/backup.example
for a version that does this.
.SH SOURCE
.B \*9/src/cmd/venti/srv
.SH SEE ALSO
.IR venti (7),
.IR venti (8)
.SH BUGS
.I Wrarena
can't read a pipe or network connection containing an arena;
it needs a file already containing the entire arena.