The column within iostat output that shows the amount (percentage) of time spent in an involuntary wait scenario due to the hypervisor is %wa. This column shows the percentage of time that the virtual machine was waiting for a resource that was not available, such as a disk or network I/O. A high %wa value can indicate that the virtual machine is not performing as well as it could be, and that the hypervisor may be overloaded.
For example, the following iostat output shows that the virtual machine was waiting for a resource for 10% of the time:
avg-cpu: %user %nice %system %iowait %steal %idle
10.60 0.00 2.00 0.00 0.00 87.40
Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn
sda 10.00 0.00 10.00 1024000 1048576
dm-0 10.00 0.00 10.00 1024000 1048576
%wa 10.00