HP NetServer AA 4000 Reference Manual page 23

Ch 1: Architecture Overview and Terminology
synchronous. At the IOP level, due to the different spin rates of the
disk drives, the I/O is asynchronous.
The query results are eventually gathered by the CE (remember, the
CE is running the SQL server application, not the IOP) and passed
by both CEs to the SSDLs. The SSDLs both pass the network packet
to the IOPs for transmittal. And at the last instant, only one IOP
places the frame on the wire. The second IOP holds off so as to
avoid Ethernet collisions.
Network Server Division 1-17