An optional OVERFLOW parameter of the ADDVOL command lets you specify that OVERFLOW volumes are to be considered for backup or migration to migration level 1 when both the following are true:

• The file you are migrating or backing up is larger than a given size, as specified on the SETSYS ML1OVERFLOW(DATASETSIZE(dssize)) command
• DFSMShsm cannot allocate enough space on a NOOVERFLOW volume by selecting either the least used volume or the volume with the most free space.

Note that DFSMShsm will use OVERFLOW ML1 volumes for the following backup functions:

• Inline backup
• HBACKDS and BACKDS commands
• ARCHBACK macro for data sets larger than dssize K bytes

You can specify the OVERFLOW parameter as follows:

ADDVOL ML1003 UNIT(3390) -
       MIGRATION(MIGRATIONLEVEL1 OVERFLOW)