It is often used to identify performance issues with storage devices, including local disks, or remote disks accessed over network file systems such as NFS.

iostat -x displays output where each line (row) gives numerical data for one device.

This is because otherwise, the output will reflect the values over the entire timespan since the system was last rebooted.

[2] It is also advisable to disregard high values in the svc_t field for disks that have very low rates of activity (less than 5%).

This is because the fsflush process can force up the average service time when synchronising data on disk with what is in memory.