vmbackup does have the ablility to ask a processor to 'quiesce' a specific
mdisk during backup.  We seem to have avoided this problem (so far) by not
using the 191 for notebooks and giving VERY active lists their own mdisk
( we now have 6 or 7 notebook mdisks varying up to 200 cyl each )
 
Perhaps inclusion of the quiesce/resume logic would be advisable in some
future release of LISTSERV ( NJE or TCPIP ) for VM
 
There is a quiesce userexit in vmbackup that can be included to send
a unique command to LISTSERV ( i.e. whatever format/content LSOFT wants )
 
- mike