I use iostat and vmstat to measure how much CPU and storage is
used during my performance tests. Many of the database engines
have their own counters to report disk IO but it is good to use
the same measurement across engines. I use the "-k" option with
iostat so it reports KB written per second per device.
The rate of writes to storage can be overstated by a factor of two in one case and I don't think this is widely known. When TRIM is done for an SSD then the Linux kernels that I use report that as bytes written. If I create an 8G file then I will see at least 8G of writes …