BandSlim: A Novel Bandwidth and Space-Efficient KV-SSD with an Escape-from-Block Approach

The Key-Value Solid State Drive (KV-SSD) represents a significant evolution in storage device interfaces by accommodating non-page-aligned key-value pairs, a departure from conventional models. However, KV-SSDs encounter challenges as their specialized data transfer and packing requirements conflict with established storage protocols like NVMe, which are designed around fixed memory page units. This discord leads to inefficient data movement and increased NAND page write I/Os, which in turn escalates network traffic and degrades both performance and NAND efficiency. To tackle these challenges, this paper introduces BandSlim, a novel solution equipped with two methods to streamline bandwidth during I/O transmission: (i) a fine-grained inline value transfer utilizing NVMe commands for bandwidth-efficient value transfer, and (ii) a selective value packing strategy combined with a backfilling policy to reduce NAND page write I/Os. We integrated BandSlim on a state-of-the-art FPGA-based LSM-tree KV-SSD, utilizing the Cosmos+ OpenSSD platform. Our comprehensive evaluations illustrate that BandSlim achieves a remarkable reduction in PCIe traffic of up to 97.9% and NAND page write counts by up to 98.1% compared to the NVMe-based KV-SSD without employing BandSlim.