Linux

sar -p          # paging
sar -d          # disk i/o


top         # press "o", then press "N" repeatedly until "mem" is at the top, then press enter

            # In newer versions of top,  the "Cpu(s)" line at the top has an entry labeled "wa".
            # This is iowait, and indicates the amount of CPU time spent waiting for any I/O operation to finish.


iostat
iotop