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IOR is designed to measure parallel file system I/O performance at both the POSIX and MPI-IO level.  "IOR" stands  "InterleavedOrRandom,” which has very little to do with how the program works currently.   This parallel program performs writes and reads to/from files under several sets of conditions and reports the resulting throughput rates. 


Download IOR-2.10.3.tar   (Updated 12 July to correct an error in the README files; no code changes)

How to Build

MPI and MPI-IO are required in order to build and run the code. The source code used for NERSC-8/Trinity is version 2.10.3.

To build the code, cd src/C and type “make mpiio” which will build both the MPI-IO and the POSIX version of the code into the resulting executable.

The resultant executable image is the file IOR and it will need to be moved up to the “run” subdirectory..  

Compiler options, names, etc., are in the file src/C/Makefile.config. 

You can also use “make clean” in the highest level directory to remove object (.o) files. 

How to Run


    • transferSize: size (in bytes) of a single data buffer to be transferred in a single I/O call. Find the transfer size that produces the highest bandwidth results and report this transfer size. blockSize will always be equal to transferSize.
    • File access: either a single file per MPI process is read/written (called “file-per-proc”) or a single shared file for all processes is read/written (called “shared file”).
    • One of the tests will just measure throughput for a packed node.  Since that concurrency is system dependent, we refer to this concurrency as“nodesize”in italics.

These runs must be set up via a combination of input configuration files and command line options, i.e., both must be used for any given run.  One input configuration file is provided (in the “run” subdirectory) that implements these tests.  It is called: N8TrinityScript

Changes to this file are permitted only for the following four parameters:

testFile (path to data file)

hintsFileName (MPI-IO hints file)

collective (MPI-IO collective vs. independent operation mode)

segmentCount (number of segments (steps, datasets) in a file)

YOU MUST adjust the segmentCount parameter to ensure that the I/O benchmark files are not cached in DRAM (the block-buffer cache).  You must set segmentCount so that the total amount of data written is greater than 1.5 times the available memory on the compute clients involved in the test.  The total filesize is given by 

filesize = segmentCount * blocksize * concurrency

For example, the baseline filesize for the supplied script is 6.4 GB for a segmentCount of 100, and 1,000,000 byte blocksize and concurrency of 64.  The segment count should be scaled so that the total filesize written is 1.5 times the sum of DRAM available on the client nodes to defeat the client-side buffer caches.  Server buffer caches may still be used, but they must be configured as they would be for the delivered NERSC-8 and Trinity systems.

The exact execution line depends on the particular MPI implementation.  A generic execution line might be:

mpirun -np 64 ./IOR -f ./ N8TrinityScript

This command will execute IOR on 64 clients with the supplied input configuration file called “N8TrinityScript.”

A very simple, sample batch submission script (run.hopper.1) is provided in the 'run' subdirectory.

You may provide your own MPI-IO “hints” file for the MPI-IO runs, which the program will look for in a file called “hintfile” (or in a file specified by the hintsFileName keyword in the input file).  If this file is not present the program will issue warning messages that may be ignored.

For each run the program does eight repetitions of the write/read process.  The maximum values are calculated and these values are to be reported as the benchmark result.

Run Rules

 In addition to the general Trinity / NERSC-8 benchmark rules, the following also apply. 

Modifications to the benchmark are only permissible to enable correct execution on the target platform.  Any modifications must be fully documented and reported back to NERSC/ACES.  Changes related to optimization and tuning must be practical for production utilization of the filesystem.  For example, optimizations that are tuning hints that can be controlled by users on the system are permissible, but optimizations that would require superuser privilege (but are not part of the steady-state configuration of the filesystem) are not permissible. 

The intent of these benchmarks is to measure system performance for file read and write operations that access disk. Although optimizations may be possible that enable significant caching or buffering of the transferred data within system memory, and although such optimizations may be beneficial in a production environment, you are not permitted to engage in such optimizations for the benchmark runs. Consequently, the run rules are designed to defeat memory caching effects so as to measure the throughput of the underlying disk subsystem. Procedures for adjusting IOR benchmark script parameters to reduce memory-caching effects will be provided later in the document.

Required Runs

IOR will execute both read and write tests for each run, doing two repetitions of each and calculating the maximum values. The bandwidth numbers to be reported are the results listed as “Max Write” and “Max Read” measured in “MB/s”.

The vendor shall determine the file size to be used in the tests. See the description of transferSize in the How to Run section.

The following tests will be run:

    • MPI/IO file per process (e.g. N-N)
    • MPI/IO shared file (e.g. N-1)
    • POSIX I/O file per process (e.g. N-N)
    • POSIX I/O shared file (e.g. N-1)

Each of the tests previously listed will be run for the following processor/node count conditions:

a)     The number of processes on one node that yields the peak results for a single node.

b)    Process count for each node equals the number of cores on a node. Find the number of nodes that yields the peak results for the test system.

c)     Process count for each node equals the number of cores on a node. Run on the total number of nodes that exist on the test system.

d)    Process count for each node equals the number of cores on a node. Estimate the bandwidth when the test is run on all nodes that will exist on the delivered system (a projection based on data gathered). 

For more information on IOR, please read the User Guide included with the source distribution.


  It is possible to pass hints to the I/O library or file system layers following this form:    'setenv IOR_HINT__<layer>__<hint> <value>'

  For example:

   'setenv IOR_HINT__MPI__IBM_largeblock_io true'

    'setenv IOR_HINT__GPFS__important_hint true'

  or, in a file in the form:    'IOR_HINT__<layer>__<hint>=<value>'

  Note that hints to MPI from the HDF5 or NCMPI layers are of the form:

    'setenv IOR_HINT__MPI__<hint> <value>'


You must provide with your results an end-to-end description of the environment in which each benchmark was run.  This will include:

    • Client and server system configurations, including node and processor counts, processor models, memory size and speed, and OS (names and versions)
    • Storage used for global file system and storage configurations.
    • Network fabric used to connect servers, clients, and storage, including network configuration settings. 
    • Client and server configuration settings.  These should include:
      • Client and server sysctl settings
      • Driver options
      • Network interface options
      • File system configuration options
    • Compiler name and version, compiler options, and libraries used to build benchmarks.

For all runs it is required to report the maximum write and maximum read bandwidth. Write bandwidth is most important, so when in doubt report the parameters where maximum write bandwidth was achieved.

Timing Issues

The default timing function for the code is the standard C-library function gettimeofday(). This is used to measure the elapsed time of reading/writing to determine throughput.

Change Log

  • 03/29/2013
    • Initial version on this web site