After changing kernel (upgrading from ubuntu 12.04 to 13.04) Munin start warning me the disk performance, like the following image. The avg io wait r/w stay at around 30 seconds. http://picpaste.com/disk_latency-TuJXeSQS.png But strangely enough, the server is running fine and no disk performance issue encountered. When I verify it with the following command, the result seems normal. sudo ioping /dev/vda -c 30 --- /dev/vda (device 30.0 GiB) ioping statistics --- 30 requests completed in 29.0 s, 911 iops, 3.6 MiB/s min/avg/max/mdev = 363 us / 1.1 ms / 3.4 ms / 668 us Does munin reading something wrong, or did I miss something?