1. A computer program product comprising a computer readable storage medium having program instructions that execute to manage spare space in a storage device and to: determine a current write amplification based on storage writes to a media at the storage device and host writes from a host to the storage device; determine a remaining storage write rate based on maximum storage writes for the storage device minus storage writes at the storage device and a remaining duration comprising an estimated lifespan of the storage device minus a power-on duration since the storage device was powered-on; determine an adjustment to the current write amplification to produce an adjusted write amplification based on the determined remaining storage write rate and a current storage write rate of writes at the storage device; determine an adjustment to the spare space based on the adjusted write amplification, wherein the spare space comprises overprovisioned storage space not comprising user accessible storage; and initiate an operation to reconfigure the spare space and free space available to a user to adjust the spare space by the determined adjustment to the spare space.