NVMe Flash-based SSDs are widely deployed in data centers to cache working sets of large-scale web services. As data centers face increasing sustainability demands, such as reduced carbon emissions, efficient management of Flash overprovisioning and endurance has become crucial. Our analysis demonstrates that mixing data with different lifetimes on Flash blocks results in high device garbage collection costs, which either reduce device lifetime or necessitate host overprovisioning. Targeted data placement on Flash to minimize data intermixing and thus device write amplification shows promise for addressing this issue.

The tight coupling of data-intensive systems and I/O interface has been a problem for years. A database system, relying on an specific I/O backend for direct asynchronous I/Os such as libaio, inherits its limitations in terms of portability, expressiveness and performance. The emergence of high-performance NVMe Solid-State Drives (SSDs), enabling new command sets, compounds this problem. Indeed, efforts to streamline the I/O stack have led to the introduction of new, complex and idiosyncratic I/O interfaces such as SPDK, io_uring or asynchronous ioctls. What is the appropriate I/O interface for a given system? How can applications effectively leverage SSD and end-to-end I/O interface innovations? Is I/O interface lock-in a necessary evil for data-intensive systems and storage services? Our answer to the latter question is no. Our answer to the former questions is xNVMe, a cross-platform user-space library that provides I/O-interface independence to user-space software. In this paper, we present the xNVMe API, we detail its design and we show that xNVMe has a negligible cost atop the most efficient I/O interfaces on Linux, FreeBSD and Windows.