Unable to find cause of high disk I/O
I've been experiencing issues with high disk I/O on my KVM VPS recently, which has caused several excessive I/O alerts from my host (a well-known provider here on LEB/LET). In particular, there is always a constant disk read of about 7MB/s. The VPS is running Ubuntu 16.04 64-bit and has 1.5GB of RAM, of which about 2/3 is in use at any given time. Swap usage hovers between 25-100MB out of 1.2GB.
Here's the output from a single invocation of iostat, which, according to my understanding, represent running averages since boot:
Here's the I/O graph over the last 24 hours from my host's control panel:
The VPS is used for web/HTTP and PostgreSQL database. I initially suspected the Postgres database was causing issues, but I can't seem to find the source of this phantom read I/O. iotop does not provide any clues, and running iostat at 1s intervals show that disk I/O is minimal. Furthermore, vmstat shows that swap activity is minimal as well. I even considered the possibility that my host's I/O metering was buggy, but they replied that since I/O usage is read directly from the hypervisor it is impossible for their readings to be wrong.
I'm at my wit's end trying to figure this out. Does anyone have any ideas?