iostat output changes in Ubuntu 18.04

The output format has changed for iostat -kx 1 in Ubuntu 18.04. The changes include reordered columns, renamed columns and new columns. My benchmark scripts scrape this output and use it to compute efficiency metrics so I need to update the scripts to catch up to Ubuntu. I should also update them to deal with future output format changes, or better yet, just scrape /proc/diskstats directly.

Next up - I should determine whether bytes trimmed are still included in bytes written. It will be nice when the bytes trimmed column shows up in iostat but that requires kernel 4.18 or 4.19 per this and with Ubuntu 18.04 (latest LTS) I use 4.15.

This bug report explains the differences.

• rrqm/s and wrqm/s were moved from columns 2, 3 to 6, 7
• avgqu-sz was renamed to aqu-sz
• await was removed - r_await and w_await remain
• avgrq-sz was replaced by rareq-sz and wareq-sz