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I want metrics for how much writing and reading have been done to a folder.

vmstat -d gives metrics at the whole disk level. iotop will give per process rw stats.

But how can I find out how much writing has been done to a folder or file?

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  • 1
    Can't you compare the outputs of two different du -sx invocations?
    – Bratchley
    Dec 19, 2014 at 23:41
  • 3
    Related / possible duplicates: How can I monitor disk I/O in a particular directory ?, How to monitor I/O stream in a particular Linux directory or file ?
    – don_crissti
    Dec 20, 2014 at 1:24
  • You may want to clarify what "how much writing" means for you. Difference between the directory sizes before and after writing? Amount of data sent to the underlying block device?
    – peterph
    Dec 20, 2014 at 19:41
  • @don_crissti, one of those answers involved loopback mounting the directory in question - gotta love the simplicity of it.
    – rjt
    Jan 3, 2015 at 17:53
  • @peterph, one movtivation is estimating SSD longevity due to caching proxy server rewrites. Amount of data sent to an underlying block device due to /var/proxy/cache/, but not not /var/log/.
    – rjt
    Jan 3, 2015 at 18:04

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Given the clarification in the comment - the need of knowing how much data is being sent to the underlying block device (e.g. for the purposes of logging activity on SSD) - you'd need to check this in the file system driver and below (which usually is part of the kernel). Note, that just writing to a file doesn't mean the data gets really sent or even written to the device - there usually is lots of caching between the write() system call in user space and the actual bits making it into the wires connecting the hard drive to the controller.

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