lmdd - move io for performance and debugging tests
copies a specified input file to a specified output with possible
conversions. This program is primarily useful for timing I/O since it prints
out the timing statistics after completing.
- Input file is taken from name; internal is
the default. internal is a special file that acts like Sun's
/dev/zero, i.e., it provides a buffer of zeros without doing a
system call to get them.
The following file names are taken to mean the standard input: -,
0, or stdin.
- Output file is taken from name; internal is
the default. internal is a special file that acts like
/dev/null, without doing a system call to get rid of the data.
The following file names are taken to mean the standard output: -,
1, or stdout.
The following file names are taken to mean the standard error: 2, or
- Input and output block size n bytes (default 8192).
Note that this is different from dd(1), it has a 512 byte default. Also
note that the block size can be followed by 'k' or 'm' to indicate kilo
bytes (*1024) or megabytes (*1024*1024), respectively.
- If n is non zero, expect a known pattern in the file
(see opat). Mismatches will be displayed as "ERROR: off=%d want=%x
got=%x". The pattern is a sequence of 4 byte integers with the first
0, second 1, and so on. The default is not to check for the pattern.
- If n is non zero, generate a known pattern on the
output stream. Used for debugging file system correctness. The default is
not to generate the pattern.
- If n is non zero, stop at the first mismatched
value. Used with ipat.
- Skip n input blocks before starting copy.
- If n is non-zero, call fsync(2) on the output file
before exiting or printing timing statistics.
- If n is non-zero, call sync(2) before exiting or
printing timing statistics.
- This argument, by default off, turns on random behavior.
The argument is not a flag, it is a size, that size is used as the upper
bound for the seeks. Also note that the block size can be followed by 'k'
or 'm' to indicate kilo bytes (*1024) or megabytes (*1024*1024),
- If n is non-zero and mmap(2) is available, call
msync(2) to invalidate the output file. This flushes the file to disk so
that you don't have unmount/mount. It is not as good as mount/unmount
because it just flushes file pages - it misses the indirect blocks which
are still cached. Not supported on all systems, compile time option.
- If n is non-zero, print rusage statistics as well as
timing statistics. Not supported on all systems, compile time option.
- Copy only n input records.
This is the most common usage, the intent is to measure disk performance. The
disk is a spare partition mounted on /spare.
# mount /spare
# lmdd if=internal of=/spare/XXX count=1000 fsync=1
7.81 MB in 3.78 seconds (2.0676 MB/sec)
: Flush cache
# umount /spare
# mount /spare
# lmdd if=/spare/XXX of=internal
7.81 MB in 2.83 seconds (2.7611 MB/sec)
Larry McVoy, firstname.lastname@example.org