From my point of view the problem is free disk space (110 GB) is lower than dataset size (115GB). When SAS sorts it creates a new file with the extension ".lck" to write the observations in sorted order. When it's finished the unsorted file is deleted and the new file is renamed (cut off the trailing ".lck"). This means for a very short period of time you need the dateset size twice (2 x 115 GB). That's why you run in the "disk full condition". My solution is create a library on E: , move (not copy) the unsorted dataset in there, sort it there and move it back or use the out= option in proc sort to write the sorted dataset on C: directly
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