Why virtual machines need virtual storage
Consolidation is a common trend in IT environments, providing benefits such as increased resource utilisation, simplified management and lower overheads. Storage consolidation is accomplished by moving data off direct attached storage (DAS) and onto a shared pool of storage in a storage area network (SAN). Recently, server consolidation has helped to put virtualisation technologies, such as VMware Infrastructure 3 and Microsoft Virtual Server, on the map. Using such server virtualisation technology, organisations can dramatically lower their hardware footprint by converting physical servers to virtual machines which reside on a physical host. Server utilisation rates in standard physical environments generally run at around 15 percent; but using virtualisation to run multiple virtual servers on each physical machine can drive utilisation up to 70 percent and above. Furthermore, because virtual machines are files rather than physical boxes, they can easily be moved between different host machines while they are still running. With the most recent virtualisation technology, management tools include features such as automated load balancing and high availability which make the management of virtual infrastructures far simpler than that of their physical counterparts. In virtual infrastructures, computing resources can be treated as a shared pool – virtual servers can be automatically moved between physical hosts to balance workloads and extra resources can be assigned to meet changing business demands. This ability to move live running virtual machines between servers does present some interesting new challenges from a storage perspective. Significant new burdens are placed on storage - traffic loads will vary as multiple virtual and physical machines try to access data at different times. Many of the benefits of server virtualisation are nullified if storage remains physically attached to the server (as in a DAS environment). This is because where virtual machines are residing on a single server, they cannot be moved onto another host server unless the files are physically copied across to the second server’s internal storage as well. SAN environments add flexibility and eliminate most of the need for data to be copied, but administrators still have to deal with load balancing and scaling tasks. To provide the most flexible infrastructure, virtual servers need to be combined with virtual SAN storage that automates the load balancing and scaling process. Storage virtualisation seeks to simplify cumbersome tasks – like allocating storage, load balancing, configuring RAID, and backing up and restoring data. Ideally, the physical disks and complex underpinnings of the storage network are concealed from administrators and servers. Disk space is presented to the operating system as a ‘logical volume’ or shared pool that appears to be a normal disk or partition. With a layer of abstraction between storage and hosts, administrators are no longer bound to the physical dimensions of a disk or forced through complex steps to perform basic storage management tasks. Not only does virtualisation improve efficiency and productivity, it reduces the time, effort, and knowledge needed to manage storage. Since virtual server and SAN technologies vary, it is important for an organisation to implement solutions that offer all the functionality it needs. For example, it’s important that virtual machines are ‘SAN aware’ – if the virtual machines ‘know’ they are on the SAN, then SAN-based functions such as snapshot-based backups, multi-path I/O, cluster support and SAN booting will be available. If not, the virtual machines will ‘think’ they are on DAS, and many of the advanced server and SAN features will be unavailable. Organisations must also carefully consider the kind of SAN technology they implement. By far the most suitable storage technology for virtual environments is a fully virtualised iSCSI-based SAN certified for virtual server environments, which will allow virtual machines to be fluidly deployed and redeployed as needed with no disruption to operations. The fact is that an organisation will get the most out of server virtualisation if it implements storage virtualisation alongside it, and vice versa. Enterprises now have the ability to treat their infrastructures as a large pool of flexible computing resources. It does not make sense to have the potential benefits of virtualisation negated by a physical approach to storage. Having broken the traditional tie between physical hardware and the applications, operating systems and data which these machines support, virtualisation has forced a complete rethink of the way organisations approach both server and storage deployment. EqualLogic is exhibiting at Storage Expo 2007, the UK event dedicated to data storage. Now in its 7th year, the show features a comprehensive free education programme, and over 100 exhibitors at Olympia, London from 17-18th October 2007 www.storage-expo.com
•Date: 6th June 2007• Region: UK/World •Type: Article •Topic: IT continuity |
