# btrecord

## NAME



           btrecord - recreate IO loads recorded by blktrace
    


## SYNOPSIS



           **Usage:**
    
           btrecord [ _options_ ] <_dev_...>
    


## DESCRIPTION



           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_ >
           --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.
    


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