Friday, 7 July 2017

Linux: Benchmarking disk I/O and determining block size

A quick command that can be used to benchmark the disk write speed:

time sh -c "dd if=/dev/zero of=ddfile bs=8k count=250000 && sync"; rm ddfile

and with a slightly larger block size:

time sh -c "dd if=/dev/zero of=ddfile bs=16M count=10 && sync"; rm ddfile

Note: Finding the appropriate block size when working with dd will be dependant on the hardware - the block size determines how how data is kept in memory during the copy - so you can imagine that if the block size is 2G in size you would need to ensure that you have at least 2GB of free RAM. I like to start with a BS of 64k and compare it with something like 16M.

We can also test read speed suing hdparm:

hdparm -t /dev/sda1 # performs buffered test (more accurate)

hdparm -T /dev/sda1 # performs cached test

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