Storage Developer Conference

Zoned Namespaces represent the first step towards the standardization of Open-Channel SSD concepts in NVMe. Specifically, ZNS brings the ability to implement data placement policies in the host, thus providing a mechanism to lower the write-amplification factor (WAF), (ii) lower NAND over-provisioning, and (iii) tighten tail latencies. Initial ZNS architectures envisioned large zones targeting archival use cases. This motivated the creation of the "Append Command” - a specialization of nameless writes that allows to increase the device I/O queue depth over the initial limitation imposed by the zone write pointer. While this is an elegant solution, backed by academic research, the changes required on file systems and applications is making adoption more difficult. As an alternative, we have proposed exposing a per-zone random write window that allows out-of-order writes around the existing write pointer. This solution brings two benefits over the “Append Command”: First, it allows I/Os to arrive out-of-order w