=encoding utf8

=head1 NAME

blkreplay - block device testing and benchmarking tool

=head1 SYNOPSIS

B<blkreplay> [I<options>] I<device>

=head1 DESCRIPTION

B<blkreplay> is a utility driving the block layer of the operating
system while measuring latency and throughput of I/O operations
for later visualisation.

B<blkreplay> can create artificial loads (random read-write sweeps,
various kinds of overload tests) or replay natural loads which
have been recorded by blktrace or a similar utility run at
production servers.

B<blkreplay> can be used to test physical hardware, to compare
different brands of hard disks or RAID controllers, to
evaluate the effect of SSD caching, to compare different
block level transports like iSCSI vs Fibrechannel and so on.

B<blkreplay> parses the load data from stdin. To create load data from
B<blktrace> output, use B<conv_blktrace_to_load.sh> script.

=head1 OPTIONS

=over

=item Influence replay duration:

=over

=item B<--replay-start=>I<val>

start offset (in seconds, 0=from_start)

=item B<--replay-end>=I<val>

end offset (in seconds, 0=unlimited)

=item B<--replay-duration>=I<val>

alternatively specify the end offset as delta

=item B<--replay-out>=I<val>

start offset, used for output (in seconds)

=item B<--start-grace>=I<val>

start after grace period for filling the pipes (in seconds)

=back

=item Handling of conflicting I/O requests:

=over

=item B<--with-conflicts>

conflicting writes are ALLOWED (damaged I/O)

=item B<--with-drop>

conflicting writes are simply dropped

=item B<--with-partial>

partial ordering by pushing back conflicts (default)

=item B<--with-ordering>

enforce total order in case of conflicts

=item B<--strong>=I<val>

mode between 0 and 2, see docs (default=1)

=back

=item Replay parameters:

=over

=item B<--threads>=I<val>

parallelism (default=1024)

=item B<--fill-random>=I<val>

fill data blocks with random bytes (%, default=0)

=back

=item Verification modes:

=over

=item B<--no-overhead>

verify is OFF (default)

=item B<--with-verify>

verify on reads

=item B<--with-final-verify>

additional verify pass at the end

=item B<--with-paranoia>

re-read after each write (destroys performance)

=back

=item Convenience:

=over

=item B<--verbose>=I<val>

increase verbosity, show additional INFO: output

=back

=item Expert options (DANGEROUS):

=over

=item B<--o-direct>

use O_DIRECT (default)

=item B<--no-o-direct>

don't use O_DIRECT, deliver FAKE results

=item B<--o-sync>

use O_SYNC

=item B<--no-o-sync>

don't use O_SYNC (default)

=item B<--dry-run>

don't actually do I/O, measure internal overhead

=item B<--fake-io>

omit lseek() and tags, even less internal overhead

=item B<--simulate-io>=I<val>

delay value for I/O simulation (timespec I<sec.nsec>)

=item B<--ahead-limit>=I<val>

limit pipe fillahead (realtime I<sec.nsec>)

=item B<--fan-out>=I<val>

only for kernel hackers (default=4)

=item B<--no-dispatcher>

only for kernel hackers

=item B<--bottleneck>=I<val>

max #requests on dispatch

=item B<--speedup>=I<val>

speedup / slowdown by REAL factor (default=1.0)

=item B<--mmap-mode>

use mmap() instead of read() / write() [NYI]

=back

=back

=head1 AUTHORS

B<blkreplay> was written by Thomas Schoebel-Theuer. This manual page was created from B<blkreplay> documentation by Andrew Shadura.

=head1 COPYRIGHT

Copyright 2009-2012 Thomas Schoebel-Theuer

=head1 SEE ALSO

blktrace(8)

