I did a dd test on my VPSs, for your information, I am purchasing a VPS with 5 node from tmdhosting. My result:
Last login: Wed Apr 10 22:04:46 2013 from 126.96.36.199 -===================================- email@example.com [~]# dd=if/dev/zero of=test bs=512 count=2 conv=fdatasync firstname.lastname@example.org [~]# dd if=/dev/zero of=test bs=512 count=2 conv=fdatasync 2+0 records in 2+0 records out 1024 bytes (1.0 kB) copied, 51.4517 seconds, 0.0 kB/s
Amazing right? It took 51 seconds to copy 1KB!
I think this is definitely my VPS hosting provider's problem, but my VPS said that it was my website's heavy IO operation that caused this massive slow down and it has nothing to do with their slow disk, or contamination from other VPS. They insisted me to upgrade to a dedicated server, because only then, they can really confirm it is their problem and fix it.
Could my VPS hosting provider be right? How to deal with hosting provider such as this?