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blkreplay - block device testing and benchmarking tool


blkreplay [options] device


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

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.

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.

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


Influence replay duration:
start offset (in seconds, 0=from_start)

end offset (in seconds, 0=unlimited)

alternatively specify the end offset as delta

start offset, used for output (in seconds)

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

Handling of conflicting I/O requests:
conflicting writes are ALLOWED (damaged I/O)

conflicting writes are simply dropped

partial ordering by pushing back conflicts (default)

enforce total order in case of conflicts

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

Replay parameters:
parallelism (default=1024)

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

Verification modes:
verify is OFF (default)

verify on reads

additional verify pass at the end

re-read after each write (destroys performance)

increase verbosity, show additional INFO: output

Expert options (DANGEROUS):
use O_DIRECT (default)

don't use O_DIRECT, deliver FAKE results

use O_SYNC

don't use O_SYNC (default)

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

omit lseek() and tags, even less internal overhead

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

limit pipe fillahead (realtime sec.nsec)

only for kernel hackers (default=4)

only for kernel hackers

max #requests on dispatch

speedup / slowdown by REAL factor (default=1.0)

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


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


Copyright 2009-2012 Thomas Schoebel-Theuer

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