Out-of-space condition during migration

For each data set that migrates to an ML1 volume and not into an SDSP data set, DFSMShsm chooses the ML1 volume with the lowest activity or, as a secondary consideration, the most available space. An out-of-space condition on the ML1 volumes never causes immediate migration from an ML1 volume to an ML2 volume. An out-of-space condition occurs when DFSMShsm:

• Performs migration on a volume and no space exists on any ML1 volume
• Tries to allocate the migration copy and an out-of-space failure occurs

To prevent a large amount of unproductive processing when there is little free space on any ML1, the migration of data sets—caused by an out-of-space failure—retries to the ML1 volume having the most available free space. (The activity to the volume is not considered.) If a second out-of-space condition occurs while targeting the ML1 volume that has the most free space, DFSMShsm does the following:

• If the failing data set is small (less than five tracks), and if this is the first time during this processing that a small data set did not fit on an ML1 volume, the task that encountered the out-of-space condition determines the free space on all ML1 volumes, and the migration of the data set is retried. If the task encounters the out-of-space condition again, the free space determination is not done. In this case, the volume migration is terminated and, if ML1 volumes are the only target devices for the volume migration, migration is held. If tape is being used, that part continues.
• If the data set is not small (greater than or equal to five tracks), DFSMShsm fails the migration for the data set but continues migration with the next data set on the source volume.