So far virtual machine (VM) migration has focused on transferring the run-time memory state of the VMs in local area networks (LAN). However, for wide-area network (WAN) migration it is crucial to not just transfer the VMs image but also transfer its local persistent state (its file system) and its on-going network connections. In this paper we address both: by combining a blocklevel solution with pre-copying and write throttling we show that we can transfer an entire running web server, including its local persistent state, with minimal disruption — three seconds in the LAN and 68 seconds in the WAN); by combining dynDNS with tunneling, existing connections can continue transparently while new ones are redirected to the new network location. Thus we show experimentally that by combining well-known techniques in a novel manner we can provide system support for migrating virtual execution environments in the wide area.

In many clusters today, the local disks of a node are only used sporadically. This paper describes the software support for sharing of disks in clusters, where the disks are distributed across the nodes in the cluster, thereby allowing them to be combined into a high-performance storage system. Compared to centralized storage servers, such an architecture allows the total I/O capacity of the cluster to scale up with the number of nodes and disks. Additionally, our software allows customizing the functionality of the remote disk access using a library of code modules.

This paper revisits the historical concept of link-layer, block-oriented storage networking in light of commoditybased, high-bandwidth local area networks. It examines how advances in data communication technology such as virtual LANs and switched gigabit Ethernet make it relatively simple and inexpensive to re-centralize the storage resources used by clusters of workstations and servers. In particular, the work is motivated by an interest in how to support scalable and efficient access to read-only and private read-write data such as root file systems, swap partitions, log files and static web pages. These techniques complement, but do not replace, higher level distributed file systems whose primary goal is to provide coherent access to shared read/write data. This paper describes the design and implementation of a very simple, link-layer protocol, the Ethernet Block Device (EBD), for accessing remote block devices. It compares the EBD prototype to a locally attached disk and to similar, network-based techniques that use TCP/IP such as the Linux Network Block Device (NBD), as well as higher level distributed file systems such as NFS. Functionally, the implementation is compared with a local disk to determine what restrictions and visible differences exist. The performance evaluation is based on a series of standard disk and file access benchmarks run on commodity servers and standard networking equipment. The performance results show that for large sequential reads and random reads and writes EBD generally outperforms comparative network storage technologies by 15% to 30%, and performance is best when the data set fits into the server's memory. On a benchmark that is very metadata-intensive and does small sequential operations, EBD and NBD perform similarly. On certain...

Abstract — During the past few years, large, reliable and efficient storage systems have become increasingly important in enterprise environments. Additional requirements for these environments include low installation, maintenance and administration costs. In this paper we propose a hash-based storage approach, combined with block-level operating system semantics. The experimental evaluation confirms that the proposed approach is viable and can offer a cost-effective storage solution. I.

Storage clusters try to transfer the idea of cluster computing into the storage domain and to scale capacity and performance by simply adding new cluster components. This paper presents analytical considerations on the scalability of storage clusters and presents a storage cluster architecture based on peer-to-peer computing that is able to scale up to hundreds of servers and clients. The resulting storage cluster environment has been successfully implemented and tested on a Linux based HPC-cluster. The measurement results presented in this paper demonstrate the feasibility and scalability ofthis architecture. 1.