The btrecord and btreplay tools provide the ability to
record and replay IOs captured by the blktrace utility. Attempts
are made to maintain ordering, CPU mappings and time-separation of IOs.
The blktrace utility provides the ability to collect detailed
traces from the kernel for each IO processed by the block IO layer. The
traces provide a complete timeline for each IO processed, including
detailed information concerning when an IO was first received by the block
IO layer --- indicating the device, CPU number, time stamp, IO direction,
sector number and IO size (number of sectors). Using this information,
one is able to replay the IO again on the same machine or another
set up entirely.
The basic operating work-flow to replay IOs would be something like:
-
Run blktrace to collect traces. Here you specify the
device or devices that you wish to trace and later replay IOs upon. Note:
the only traces you are interested in are QUEUE requests ---
thus, to save system resources (including storage for traces), one could
specify the -a queue command line option to blktrace.
-
While blktrace is running, you run the workload that you
are interested in.
-
When the work load has completed, you stop the blktrace utility (thus saving all traces over the complete workload).
-
You extract the pertinent IO information from the traces saved by
blktrace using the btrecord utility. This will parse
each trace file created by blktrace, and crafty IO descriptions
to be used in the next phase of the workload processing.
-
Once btrecord has successfully created a series of data
files to be processed, you can run the btreplay utility which
attempts to generate the same IOs seen during the sample workload phase.
OPTIONS
-d <dir>
--input-directory=<dir>
Set input directory.
This option requires a single parameter providing the directory
name for where input files are to be found. The default directory is the
current directory (.).
-D <dir>
--output-directory=<dir>
Set output directory.
This option requires a single parameter providing the directory
name for where output files are to be found. The default directory is the
current directory (.).
-F
--find-traces
Find trace files automatically
This option instructs btreplay to go find all the trace files in the
directory specified (either via the -d option, or in the default
directory (.).
-h
--help
Show help and exit.
-V
--version
Show version number and exit.
-m <nanoseconds>
--input-base=<nanoseconds>
The -m option requires a single parameter which specifies an
amount of time (in nanoseconds) to include in any one bunch of IOs that
are to be processed. The smaller the value, the smaller the number of
IOs processed at one time --- perhaps yielding in more realistic replay.
However, after a certain point the amount of overhead per bunch may result
in additional real replay time, thus yielding less accurate replay times.
The default value is 10,000,000 nanoseconds (10 milliseconds).
-M <num>
--max-pkts=<num>
Set maximum number of packets per bunch.
The -M option requires a single parameter which specifies the
maximum number of IOs to store in a single bunch. As with the -m
option, smaller values may or may not yield more accurate replay times.
The default value is 8, with a maximum value of up to 512 being supported.
-o <basename>
--output-base=<basename>
Set base name for output files.
Each output file has 3 fields:
1.
Device identifier (taken directly from the device name of the
blktrace output file).
2.
btrecord base name --- by default ``replay''.
3.
The CPU number (again, taken directly from the
blktrace output file name).
This option requires a single parameter that will override the default name
(replay), and replace it with the specified value.
-v
--verbose
Enable verbose output.
This option will output some simple statistics at the end of a successful
run. Example output is: