Differentiated storage services

Abstract

This article presents a Differentiated Storage Services architecture for file and storage systems. By classifying data at the block-level, a filesystem can request that different classes of data (e.g., file, directory, executable, text) be handled with different policies (e.g., low-latency versus highbandwidth), and it is left to the storage system to enforce these policies. Our approach assumes that an I/O classifier can be included in-band with each I/O request (e.g., using a field in the SCSI block command set) and that the policy for each class can be specified out-of-band through the management interface of the storage system. We describe our prototypes based on Linux Ext3, Windows NTFS, and hybrid storage systems composed of rotating and solid-state disks. With very little modification, filesystems can identify latency sensitive I/O classes (e.g., small files, directories, metadata, and the journal) and request that the storage system provision the solid-state storage for just these classes; and this is simply one of many possibilities. As part of our ongoing work, across a variety of file and storage systems, we are exploring other policies and mechanisms that can be used to improve application performance, reliability, and security.