Recently, adoption of Flash based devices has become increasingly common in all forms of computing devices. Flash devices have started to become more economically viable for large storage installations like datacenters, where metrics like Total Cost of Ownership (TCO) are of paramount importance. Flash devices suffer from write amplification (WA), which, if unaccounted, can substantially increase the TCO of a storage system. In this paper, we develop a TCO model for Flash storage devices, and then plug a Write Amplification (WA) model of NVMe SSDs we build based on empirical data into this TCO model. Our new WA model accounts for workload characteristics like write rate and percentage of sequential writes. Furthermore, using both the TCO and WA models as the optimization criterion, we design new Flash resource management schemes (MINTCO) to guide datacenter managers to make workload allocation decisions under the consideration of TCO for SSDs. Experimental results show that MINTCO can reduce the TCO and keep relatively high throughput and space utilization of the entire datacenter storage.