I. Introduction
Meta deploys large-scale distributed storage services across datacenters. Storage applications are often categorized based on the type and temperature of the data stored: hot, warm, and cold data. At Meta, we have an exabyte-scale distributed file system, known as Tectonic [1]. Tectonic has tenants that include a warm Binary Large Object (BLOB) storage tier and a data warehouse tier. The warm BLOB tier is used for external media storage (photos, videos, documents), and internal application data (traces, heap dumps, logs) [2]. The data warehouse tier is designed to store data analytics for business intelligence, and objects such as massive map-reduce tables, snapshots of the social graph, and AI training data and models. Both tiers run on specialized storage servers containing Hard Disk Drives (HDDs), also known as Just-a-Bunch-of-Drives (JBODs) [3]. In industry, HDDs are widely used as either a boot device or a data device. The HDDs discussed in this paper are used as data devices. In our infrastructure, one compute module facilitates concurrent I/O across all HDDs in a JBOD.