Re: IO scheduler recommendation

IO scheduler is more of an OS thing and not a DB thing. Once the DB (be it Postgresql or any other) has submitted IO to OS it is up to the OS to make sure it is written in the fastest possible manner.

In RHEL 6, CFQ was the default and starting RHEL 7, Deadline is the default (I don’t know exactly why was the default changed). However, across rhel 6 & 7 it is suggested to have deadline for db environments. But what I separately read is that if the server is a VM, then NOOP is the best scheduler because you don’t want the VM as well as the host, both to be scheduling IO which can actually work against. In that case, let the VM not do anything, instead let the host do the scheduling.