Explanation
DFSMShsm is processing a large quantity
of volumes for on-demand migration. The number of volumes that have
exceeded the high threshold has reached nnnnn. nnnnn is
equal or greater than a user specified notification limit that was
specified by using the SETSYS ODMNOTIFICATIONLIMIT command. 
System action
DFSMShsm processing continues.
Operator response
Notify the system programmer.
System programmer response
Analyze the threshold and SMS environment settings for DFSMShsm to determine why DFSMShsm is processing a large quantity of volumes for on-demand migration.
The notification limit for volumes being processed by on-demand migration can be changed by using the SETSYS ODMNOTIFICATIONLIMIT command. For more information about setting the on-demand migration notification limit, see the SETSYS command in z/OS DFSMShsm Storage Administration.
Source
DFSMShsm