bstream(1) bstream(1)
bstream - many buffered filter
bstream [-n bufs] [-b size] [-ltrvd] [-s count] [-i file] [-o file]
This command is a filter which buffers input from the input file and
writes it to the output file. The command is especially useful for
reading from or writing to streaming tape drives, where bstream can be
used as a speed matching program to keep the tape streaming as much as
possible.
If input or output files are not specified, then bstream simply copies
the standard input to the standard output through multiple buffers. A
tape can be written to or read from in this manner, but bstream will not
be able to handle multiple tape copies. If multiple tapes are involved,
explicitly specifying the tape device via the -i or -o options will
enable bstream to recover from end of medium indications and request a
new tape.
The following options are supported:
-b size specifies the size (in 1024-byte units) of buffer to use. The
default size is 64K bytes, however any size up to the maximum
allowable shared memory segment size for the system is allowed.
-n cnt Sets the number of buffers to use. More than two buffers can
improve performance and make the tape more likely to stream. A
minimum of two and a maximum of six is enforced. The default
value is set to four.
-l Attempt to lock the shared memory buffers into physical memory.
This will not be possible unless the command is run by the
superuser.
-t Attempt to lock program image and stack in physical memory.
This will not be possible unless the command is run by the
super user. The nice value of the bstream process is also
decreased, increasing its scheduling priority.
-r Report a summary of the byte throughput achieved by bstream for
the entire transfer as well as for each individual tape if
multiple tapes are involved.
-v Reports each i/o that is done (very verbose).
-d Reports very verbose debugging information.
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bstream(1) bstream(1)
-s count Report a summary of the byte throughput achieved by bstream
every count buffers, for both input and output.
-i file Specify the input file as an explicit filename, allowing
recovery from end-of-medium conditions on tapes. The user will
be prompted for a new tape.
-o file Specify the output file as an explicit filename, allowing
recovery from end-of-medium conditions on tapes. The user will
be prompted for a new tape.
To copy a filesystem onto multiple tapes:
tar cf - * | bstream -o/dev/tape
Recovering an image from tape is just as easy:
bstream -i/dev/tape | tar xf -
There is a subtle issue involving tapes that should be understood when
using bstream with a tape device. Usually, a tape device requires that
the tape be written in even multiples of the block size. When bstream is
used as a streaming filter (see the above examples) this is not a
problem, since both tar(1) and cpio(1) block the output on natural tape
boundaries. To protect the user, bstream will round the final write to
tape up to the nearest tape blocksize boundary, fill the residual of the
last block with zeros, and print a warning message if rounding up was
needed. bstream should always be used with a formatter program such as
tar or cpio when writing to a tape device, since rounding up and filling
may have unpredictable effects on programs expecting a simple byte
stream. No rounding or filling is done when output is not directed to a
tape device.
bstream runs only on Silicon Graphics 4D series workstations. On an
unloaded 4D60, bstream can stream the tape 70 to 80% of the time,
achieving byte transfer rates around 70K bytes per second.
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