Linux high IOwait is a common Linux performance issue. Today we will look at what iowait means and what contributes to this problem. Hope this can give you more ideas about high IOwait issue.
High IOwait on Linux
The iowait column on top command output shows the percentage of time that the processor was waiting for I/O to complete. It indicates that the system is waiting on disk or network IO. Because the system is waiting on those resources, it can not fully utilize the CPU.
The process will get "stuck" in D state because of disk io or NFS io. Processes accessing hard NFS mounts will also be put into D state while they wait for the I/O to return - thus a hard NFS mount from a machine that has dropped off of the network can cause processes to go into D state.
High IOWait usually means that your disk subsystem or network storage is overworked.This can occur due to hardware problems (the kernel is waiting for something from a device that never comes) or from kernel-related issues (driver bugs that cause a system call to never return).