I left a set of 4 UML instances running overnight and noticed that in the morning my computer was not very responsive (every application I tried to interact with seemed slow).  vmstat reported 96% IO wait (wa%).

Does it make sense that leaving UML instances running would raise this statistic over time?  The UMLs were very lightly loaded.

Why would having a large wa% make the system unresponsive?  I must not understand what wa really means. I would have thought that one process spending a long time waiting for IO would not affect other processes.  In other words, one process is only waiting for IO if no other process needs the time while it is waiting.  It is certain type of idleness.

What am I missing?