Emerald Tiers: Focusing on SSD+MAID Through a Green Lens
Zhaokang Ke, Jim Diehl, Ya-Shu Chen, David H. C. Du · 2025
As the volume of retained data continues to increase, it is important to design primary storage systems that efficiently respond to access requests while also providing strong sustainability by reducing carbon emissions. Just over two decades ago, the Massive Arrays of Idle Disks (MAID) architecture was introduced as an energy-efficient alternative to traditional HDD-based always-on storage, employing aggressive spin-down strategies to reduce power consumption. However, high access latencies and hardware limitations led to its decline. In this work, we propose a tiered SSD+MAID storage model that combines the low-latency advantages of SSDs with the energy and carbon efficiency of a MAID system, thus offering a modern alternative to MAID while achieving lower carbon emissions than all-SSD storage. To assess the sustainability impact of such a tiered storage system, we develop a comprehensive carbon emission model that incorporates access patterns, update behaviors, and HDD spin-up dynamics. This model captures both operational and embodied carbon costs, enabling evaluations of primary storage with sustainability in mind. Through real-world workloads, we evaluate the proposed SSD+MAID system and show that it can provide a good trade-off between performance, price, and sustainability.