Flexible allocation and space management in storage systems

In this dissertation, we examine some of the challenges faced by the emerging networked storage systems. We focus on two main issues. Current file systems allocate storage statically at the time of their creation. This results in many suboptimal scenarios, for example: (a) space on the disk is not allocated well across multiple file systems, (b) data is not organized well for typical access patterns. We propose Virtual Allocation for flexible storage allocation. Virtual allocation separates storage allocation from the file system. It employs an allocate-on-write strategy, which lets applications fit into the actual usage of storage space without regard to the configured file system size. This improves flexibility by allowing storage space to be shared across different file systems. We present the design of virtual allocation and an evaluation of it through benchmarks based on a prototype system on Linux. Next, based on virtual allocation, we consider the problem of balancing locality and load in networked storage systems with multiple storage devices (or bricks). Data distribution affects locality and load balance across the devices in a networked storage system. We propose user-optimal data migration scheme which tries to balance locality and load balance in such networked storage systems. The presented approach automatically and transparently manages migration of data blocks among disks as data access patterns and loads change over time. We built a prototype system on Linux and present the design of user-optimal migration and an evaluation of it through realistic experiments

The Umbrella File System: Storage Management Across Heterogeneous Devices

With the advent of Flash based solid state devices (SSDs), the differences in physical devices used to store data in computers are becoming more and more pronounced. Effectively mapping the differences in storage devices to the files, and applications using the devices, is the problem addressed in this dissertation. This dissertation presents the Umbrella File System (UmbrellaFS), a layered file system designed to effectively map file and device level differences, while maintaining a single coherent directory structure for users. Particular files are directed to appropriate underlying file systems by intercepting system calls connecting the Virtual File System (VFS) to the underlying file systems. Files are evaluated by a policy module that can examine both filenames and file metadata to make decisions about final placement. Files are transparently directed to and moved between appropriate file systems based on their characteristics. A prototype of UmbrellaFS is implemented as a loadable kernel module in the 2.4 and 2.6 Linux kernels. In addition to providing the ability to direct files to file systems, UmbrellaFS enables different decisions at other layers of the storage stack. In particular, alternate page cache writeback methods are presented through the use of UmbrellaFS. A multiple queue strategy based on file sequentiality and a sorting strategy are presented as alternatives to standard Linux cache writeback protocols. These strategies are implemented in a 2.6 Linux kernel and show improvements in a variety of benchmarks and tests

Interposed Request Routing for Scalable Network Storage

This paper presents Slice, a new storage system architecture for highspeed LANs incorporating network-attached block storage. Slice interposes a request switching filter -- called a /proxy -- along the network path between the client and the network storage system (e.g., in a network adapter or switch). The purpose of the/proxy is to route requests among a server ensemble that implements the file service. We present a prototype that uses this approach to virtualize the standard NFS file protocol to provide scalable, high-bandwidth file service to ordinary NFS clients. The paper presents and justifies the architecture, proposes and evaluates several request routing policies realizable within the architecture, and explores the effects of these policies on service structur

Interposed Request Routing for Scalable Network Storage

This paper explores interposed request routing in Slice, a new storage system architecture for highspeed networks incorporating network-attached block storage. Slice interposes a request switching filter---called a proxy---along each client's network path to the storage service (e.g., in a network adapter or switch). The proxy intercepts request traffic and distributes it across a server ensemble. We propose request routing schemes for I/O and file service traffic, and explore their effect on service structure. The Slice prototype uses a packet filter proxy to virtualize the standard Network File System (NFS) protocol, presenting to NFS clients a unified shared file volume with scalable bandwidth and capacity. Experimental results from the industry-standard SPECsfs97 workload demonstrate that the architecture enables construction of powerful network-attached storage services by aggregating cost-effective components on a switched Gigabit Ethernet LA