- blktrace.git
- man btreplay
- /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.
btreplay [ 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
-c <num>
--cpus=<num>
Set number of CPUs to use.
-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 (.).
-F
--find-records
Find record files automatically This option instructs btreplay to
go find all the record files in the directory specified (either via t
he -d option, or in the default directory (.).
-h
--help
Show help and exit.
-i <basename>
--input-base=<basename>
Set base name for input files. Each input 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.
-I <num>
--iterations=<num>
Set number of iterations to run. This option requires a single
parameter which specifies the number of times to run through
the input files. The default value is 1
-M <filename>
--map-devs=<filename>
Specify device mappings. This option requires a single
parameter which specifies the name of a file contain device
mappings. The file must be very simply managed, with just two
pieces of data per line:
- The device name on the recorded system (with the '/dev/'
removed).
Example: /dev/sda would just be sda.
- The device name on the replay system to use (again,
without the '/dev/' path prepended).
An example file for when one would map devices /dev/sda
and /dev/sdb on the recorded system to dev/sdg and sdh
on the replay system would be:
sda sdg
sdb sdh
The only entries in the file that are allowed are these two
element lines — we do not (yet?) support the notion of blank
lines, or comment lines, or the like.
The utility allows for multiple -M options to be supplied on the
command line.
-N
--no-stalls
Disable pre-bunch stalls. When specified on the command line,
all pre-bunch stall indicators will be ignored. IOs will be replayed
without inter-bunch delays.
-x <factor>
--acc-factor=<factor>
Specify acceleration factor. Default value is 1 (no acceleration).
-v
--verbose
Enable verbose output. When specified on the command line, this
option instructs btreplay to store information concerning each stall
and IO operation performed by btreplay. The name of each file so
created will be the input file name used with an extension of .rep
appended onto it. Thus, an input file of the name sdab.replay.3 would
generate a verbose output file with the name sdab.replay.3.rep in the
directory specified for input files.
In addition, btreplay will also output to stderr the names of the input
files being processed.
-V
--version
Show version number and exit.
-W
--write-enable
Enable writing during replay. As a precautionary measure, by
default btreplay will not process write requests. In order to
enable btreplay to actually write to devices one must explicitly
specify the -W option.