In this example we run pgbench with a scale factor of 1000 which equates to a database size of around 15GB. The linux VM has 32G RAM, so we don’t expect to see many reads.
Using prometheus with the Linux node exporter we can see the disk IO pattern from pgbench. As expected the write pattern to the log disk (sda) is quite constant, while the write pattern to the database files (sdb) is bursty.
I had to tune the parameter checkpoint_completion_target from 0.5 to 0.9 otherwise the SCSI stack became overwhelmed during checkpoints, and caused log-writes to stall.