A method for execution by a storage unit includes identifying, from a plurality of memory devices of the storage unit, a first memory device that is designated for storage of a first data slice to be written of the storage unit based on determining a slice name of the first data slice compares favorably to a namespace assigned to the first memory device. A function is performed on the slice name of the first data slice to identify a second memory device from the plurality of memory devices of the storage unit for temporary storage the first data slice in response to determining that the first memory device is unavailable and the first data slice is stored in the second memory device in response. The first data slice is migrated to storage in the first memory device in response to determining that the first memory device is available.