- blktrace.git
- man btrecord
- /usr/share/doc/blktrace/btreplay.pdf
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.
btrecord [ options ] <dev...>
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>
--max-bunch-time=<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:
sdab:0: 580661 pkts (tot), 126030 pkts (replay), 89809 bunches, 1.4 pkts/bunch
sdab:1: 2559775 pkts (tot), 430172 pkts (replay), 293029 bunches, 1.5 pkts/bunch
sdab:2: 653559 pkts (tot), 136522 pkts (replay), 102288 bunches, 1.3 pkts/bunch
sdab:3: 474773 pkts (tot), 117849 pkts (replay), 69572 bunches, 1.7 pkts/bunch
The meaning of the columns is:
1. The first field contains the device name and CPU identifier.
Thus: sdab:0: means the device sdab and traces on CPU 0.
2. The second field contains the total number of packets
processed for each device file.
3. The next field shows the number of packets eligible for replay.
4. The fourth field contains the total number of IO bunches.
5. The last field shows the average number of IOs per bunch recorded.