A few weeks ago we decided to upgrade the firmware on couple of storage systems. Everything seemed to go as planned but after the upgrade we started to notice some latency issues.
I won’t go into detail what was wrong (hint, HDD firmware can cause some serious issues!)- but this tool, STOR2RRD has saved us loads and loads of time – and is as simple as any storage monitoring tool can be. It ain’t perfect but it pointed us in the right direction and helped with getting this specific issue solved.
Cannot recommend this tool enough (and it is free and open source licensed under the GPL v3!).