iozone benchmark doc. You may use one or more of the following keywords [iozone msword pdf ozone] to. IOzone. IOzone is a file system benchmark utility. Originally made by William Norcott, SCO OpenServer, Solaris, Mac OS X, Windows (95/98/Me/NT/2K/XP). I wrote this book using Microsoft Word 98 for the Macintosh. Hence, the screen shots, menus, etc. might look a little different if you are using a different version or .

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This test measures the performance of writing a file using the library function fwrite. You will need to select this when graphing as the default in Excel is row oriented data. If the poor system administrator ever installs an application that likes to read or write files in a record size iozohe Kbytes to 1 Mbyte his users will probably take him out back for a conference.

If you wish to get accurate results for the entire range of performance for a platform you need to make sure that the maximum file size that will be tested is bigger than the buffer cache. The second field is the path, on the client, for the working directory where Iozone will execute.

This test measures the performance of reading a file using the library function fread. If the size of the spot is bigger than the CPU data cache but still fits in the TLB then one gets a different level of performance. One may also specify -y k size in Kbytes or -y m size in Mbytes or -y g size in Gbytes.

This option allows iosone types of applications to be simulated. A sign in column zero is a comment line. If you don’t know how big the buffer cache is, or if it is a dynamic buffer cache then just set the maximum file size to be greater than the total physical memory that is in the platform.


Notice the performance dip at record sizes of Kbytes.

Notice that the processor cache is now very important and causes the sharp peak. This test maword the performance of reading a file backwards. This test measures the performance of writing a file that already exists. Only available on some platforms. The —a option in Iozone tells Iozone to discontinue use of transfer sizes less iosone 64k once the file size is 32MB or bigger.

This is useful only if you suspect that close is broken in the operating system currently under test. This run was taken with the —a iozonne. Each line has three fields. Leave them present in the filesystem. This is useful for finding if certain offsets have very high latencies. One can see from the data the impacts of the extent allocations for extent based filesystems with this option.

This hot spot can have very interesting behaviors.


The 3D graphs are column oriented. The benchmark generates and measures a variety of file operations. Msqord the re-read latency graph one can clearly see the client side cache that is in NFS Version 3.

It is normal for the rewrite performance to be higher than the performance of writing a new file.

An example would be to have an array in memory that is also being maintained as a file in the files system. Another example is when the filesystem is mounted from a remote machine. Tells the VXFS filesystem that all operations to the file are to bypass the buffer cache and go directly to disk.

If the system would have been characterized before it was purchased it would never have made it into the building.

What is “iozone”

This may be needed if the client is running NFS version 3. The code starts all threads or processes and then stops them on a barrier. Iozone —a If you wish to generate graphs then you may wish to turn on Excel mode. When running throughput tests this option allows the user to specify the least number of processes or threads to start.


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Iozone will generate an Excel compatible report to standard out. Iozonw the next dialog box pops up you need to select “Columns”.

This option is useful if one has taken a system call trace of the application that is of interest. Use —az —i 0 —i 1 instead. Here one can see that there are some file sizes and some record sizes that have very mwword performance.

This saves quite a bit of time. This is generally sufficient but for some very large systems you may need to use the —g option to increase the maximum file size. The —a option will automatically stop using transfer sizes less than 64k once the file size is 32 MB or larger. This test measures the performance of writing a file with accesses being made to random locations within the file. This is handy if an application wishes to treat files as chunks of memory.

This test measures the performance of reading a file that was recently read. Notice the ridge that runs from the top left to the lower right down the center of the graph.

Processor cache size configurable.

The file contains one line for each client. Just copy Iozone to wherever you wish to test the filesystem performance and then run it. Before you run Iozone please read the run rules at the bottom of this document.