Tag: fio
The real-world achievable SSD performance will vary depending on factors like IO size, queue depth and even CPU clock speed. It’s useful to know what the SSD is capable of delivering in the actual environment in which it’s used. I always start by looking at the performance claimed by the manufacturer. I use these figures…
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The vertica vioperf tool is used to determine whether the storage you are planning on using is fast enough to feed the vertica database. When I initially ran the tool, the IO performance reported by the tool and confirmed by iostat was much lower than I expected for the storage device (a 6Gbit SATA device…
Read More →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…
Read More →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)
Read More →Often we are presented with a vCenter screenshot, and an observation that there are “high latency spikes”. In the example, the response time is indeed quite high – around 80ms.
Read More →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…
Read More →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…
Read More →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…
Read More →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…
Read More →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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