Patent ID: 7404039

Claim:
A method for reducing contention between migration of data and space allocation in a hierarchal storage subsystem, comprising: (a) designating a plurality of volumes as a storage group for Level 0 storage; (b) establishing a first threshold for the storage group; (c) establishing a second threshold for each volume in the storage group; (d) allocating space for a data set to a first volume of the storage group: (e) storing the data set to the first volume; (f) comparing the first threshold with a total amount of space used by all data sets stored to all volumes in the storage group; (g) if the first threshold has been reached: identifying the volume of the plurality of volumes having the least amount of free space of all volumes in the storage group (“second volume”); and migrating data sets to a Level 1 storage from the storage group beginning with data sets stored in the second volume and continuing until the total amount of space used by all of the data sets stored in the second volume is less than or equal to the second threshold established for the second volume; (h) repeating steps (e) through (g) if the first threshold has not been reached; (i) identifying the volume of the plurality of volumes, other than the second volume, having the most free space of all volumes in the storage group (“third volume”); and (j) allocating space for a new data set to the third volume, whereby a risk is reduced that the allocation will be to space of the second volume from which data sets are being migrated.