Tag: fio

Working with fio “distribution /pereto” parameter
By: Date: November 12, 2018 Categories: Nutanix,X-Ray Tags: ,

The fio Pareto parameter allows us to create a workload, which references a very large dataset, but specify a hotspot for the access pattern.  Here’s an example using the same setup as the ILM experiment, but using a Pareto value of 0:8.  My fio file looks like this.. [global] ioengine=libaio direct=1 time_based norandommap random_distribution=pareto:0.8 The…

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The return of misaligned IO
By: Date: May 25, 2017 Categories: Debugging Tags: , ,

We have started seeing misaligned partitions on Linux guests runnning certain HDFS distributions.  How these partitions became mis-aligned is a bit of a mystery, because the only way I know how to do this on Linux is to create a partition using old DOS format like this (using -c=dos  and -u=cylinders) 

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Creating compressible data with fio.
By: Date: October 18, 2016 Categories: fio Tags: , , ,

Today I used fio to create some compressible data to test on my Nutanix nodes.  I ended up using the following fio params to get what I wanted.   buffer_compress_percentage=50 refill_buffers buffer_pattern=0xdeadbeef buffer_compress_percentage does what you’d expect and specifies how compressible the data is refill_buffers Is required to make the above compress percentage do what you’d…

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Specifying Drive letters with fio for Windows.
By: Date: October 5, 2016 Categories: fio Tags: , , ,

Simple fio file for using Drive letters on Windows. This will create a file called “fiofile” on the F:\ Drive in Windows.  Notice that the specification is “Driveletter” “Backslash” “Colon” “Filename” In fio terms we are “escaping” the “:” which fio traditionally uses as a file separator. [global] bs=1024k size=1G time_based runtime=30 rw=read direct=1 iodepth=8…

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Things to know when using vdbench.
By: Date: September 21, 2015 Categories: vdbench Tags: ,

Recently I found that vdbench was not giving me the amount of outstanding IO that I had intended to configure by using the “threads=N” parameter. It turned out that with Linux, most of the filesystems (ext2, ext3 and ext4) do not support concurrent directIO, although they do support directIO. This was a bit of a…

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Multiple devices/jobs in fio
By: Date: June 17, 2014 Categories: fio Tags: ,

If your underlying filesystem/devices have different response times (e.g. some devices are cached – or are on SSD) and others are on spinning disk, then the behavior of fio can be quite different depending on how the fio config file is specified.  Typically there are two approaches 1) Have a single “job” that has multiple…

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Here be Zeroes
By: Date: June 12, 2014 Categories: Debugging Tags: ,

Many storage devices/filesystems treat blocks containing nothing but zeros in a special way, often short-circuiting reads from the back-end.  This is normally a good thing but this behavior can cause odd results when benchmarking.  This typically comes up when testing against storage using raw devices that have been thin provisioned. In this example, I have several…

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