1. A method for depopulation of storage ranks, the method comprising: identifying, by one or more computer processors, at least one source rank selected for depopulation in a storage pool; identifying, by one or more computer processors, one or more source extents for depopulation, wherein the identified one or more source extents belongs to the identified at least one source rank selected for depopulation; obtaining, by one or more computer processors, for each identified source extent of the identified one or more source extents to be depopulated, at least one I/O workload; sorting, by one or more computer processors, the one or more source extents to be depopulated, based at least in part on the at least one I/O workload for each identified source extent of the identified one or more source extents; determining, by one or more computer processors, a state of a short-term I/O workload for each source extent; determining, by one or more computer processors, a state of a long-term I/O workload for each source extent; dividing, by one or more computer processors, all source extents to be depopulated into four groups, wherein the four groups comprise short-term hot, short-term cool, long-term hot, long-term cool, with different priorities based on the determined state of the short-term I/O workload and the determined state of the long-term I/O workload for each source extent; sorting, by one or more computer processors, all source extents of the determined four groups based on a value of the short-term I/O workload for each source extent; generating, by one or more computer processors, a migration plan based on the sorted all source extents, wherein the migration plan identifies a target extent for each source extent for migration; and executing, by one or more computer processors, the generated migration plan.