Circular SSDs enabled by Recoverable 3D Flash Memory

Achieving net-zero emissions is becoming increasingly important in order to realize a sustainable society. Data centers, which are facing an ever-increasing demand, consume 1% to 3% of the world's electricity supply and are responsible for 2% of global carbon emissions [1]. Even with 70% to 75% renewable energy, nearly half of carbon emissions associated with data centers come from Scope3, which is supply chain emissions. Within scope3, server equipment is responsible for a significant portion [2]. In the case of server equipment, the CO2 emissions from the manufacturing are comparable to those from their operation [3]. For computing servers, SSDs account for 35% of carbon emissions from their manufacturing [4]. This is the second largest percentage following DRAM, which accounts for 40%. In SSDs, 3D flash memory is utilized for the data storage. Due to the increasing number of stacked word line (WL)-layers of 3D flash memory for capacity expansion, the growing number of processing steps rapidly increases the CO2 emissions from manufacturing SSDs [4], [5]. For example, the expected CO2 emissions for 128 WL-layers and 1024 WL-layers are 500 kg and 2,250 kg respectively [6]. In this way, we are facing two conflicting demands: CO2 reduction and further data capacity expansion of SSD. To overcome this challenge, we believe that new technologies for reusing SSDs, or in other words extending their lifetime, will become increasingly important in the near future. Indeed, in the case of DRAM, older DDR4 modules are already being reused and connected to PCIe5 via CXL controller cards [4]. In this paper, we describe the technology to reuse SSD.