Performance of Disk I/O operations during the Live Migration of a Virtual Machine over WAN
Abstract: Virtualization is a technique that allows several virtual machines (VMs) to run on a single physical machine (PM) by adding a virtualization layer above the physical host's hardware. Many virtualization products allow a VM be migrated from one PM to other PM without interrupting the services running on the VM. This is called live migration and offers many potential advantages like server consolidation, reduced energy consumption, disaster recovery, reliability, and efficient workflows such as "Follow-the-Sun''. At present, the advantages of VM live migration are limited to Local Area Networks (LANs) as migrations over Wide Area Networks (WAN) offer lower performance due to IP address changes in the migrating VMs and also due to large network latency. For scenarios which require migrations, shared storage solutions like iSCSI (block storage) and NFS (file storage) are used to store the VM's disk to avoid the high latencies associated with disk state migration when private storage is used. When using iSCSI or NFS, all the disk I/O operations generated by the VM are encapsulated and carried to the shared storage over the IP network. The underlying latency in WAN will effect the performance of application requesting the disk I/O from the VM. In this thesis our objective was to determine the performance of shared and private storage when VMs are live migrated in networks with high latency, with WANs as the typical case. To achieve this objective, we used Iometer, a disk benchmarking tool, to investigate the I/O performance of iSCSI and NFS when used as shared storage for live migrating Xen VMs over emulated WANs. In addition, we have configured the Distributed Replicated Block Device (DRBD) system to provide private storage for our VMs through incremental disk replication. Then, we have studied the I/O performance of the private storage solution in the context of live disk migration and compared it to the performance of shared storage based on iSCSI and NFS. The results from our testbed indicate that the DRBD-based solution should be preferred over the considered shared storage solutions because DRBD consumed less network bandwidth and has a lower maximum I/O response time.
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