Hybrid Data Reliability for Emerging Key-Value Storage Devices

Rapid growth in data storage technologies created the modern data-driven world. Modern workloads and application have influenced the evolution of storage devices from simple block devices to more intelligent object devices. Emerging, next-generation Key-Value (KV) storage devices allow storage and retrieval of variable-length user data directly onto the devices and can be addressed by user-desired variable-length keys. Traditional reliability schemes for multiple block storage devices, such as Redundant Array of Independent Disks (RAID), have been around for a long time and used by most systems with multiple devices.

Now, the question arises as to what an equivalent for such emerging object devices would look like, and how it would compare against the traditional mechanism. In this paper, we present Key-Value Multi-Device (KVMD), a hybrid data reliability manager that employs a variety of reliability techniques with different trade-offs, for key-value devices. We present three stateless reliability techniques suitable for variable length values, and evaluate the hybrid data reliability mechanism employing these techniques using KV SSDs from Samsung. Our evaluation shows that, compared to Linux mdadm-based RAID throughput degradation for block devices, data reliability for KV devices can be achieved at a comparable or lower throughput degradation. In addition, the KV API enables much quicker rebuild and recovery of failed devices, and also allows for both hybrid reliability configuration set automatically based on, say, value sizes, and custom per-object reliability configuration for user data.