1. A system, comprising: a device that includes a processor and a memory, the memory including instructions executable by the processor, the instructions including instructions for: receiving a command to alter data storage in a cluster, along with parameters for executing the command; obtaining information relating to one or more volumes in the cluster and information relating to devices in the cluster; generating a formal description of a placement function that maps one or more object identifiers to a storage device set; and generating placement function code by compiling the formal description of the placement function to computer-executable code.