Virtual target
- Article 1 of 2
- Information Unbound, October 2006
Virtualisation is the key component necessary to deliver optimised storage area networks.
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Fabric- or switch-level virtualisation is garnering the most interest since it’s possible to overcome most of these problems, even if it does require expensive hardware. “There’s general interest from my customers,” says Andy Holpin, storage solutions consultant at services company Morse. “I’ve been talking to one large customer who wanted a proof of concept: that it was possible to virtualise and migrate data between different types of storage, mirroring between an EMC and a Hitachi and so on.”
Virtualisation can either be done inband or out-of-band. Inband requires hardware that can sit between all the network’s storage arrays and servers and mediate data transfer between them using standard SCSI commands. If the hardware isn’t capable of moving data at the same speed as the rest of the SAN, this can affect scalability and throughput, so the requisite hardware has to contain considerably processing power, pushing up costs. Indeed, Morse’s Andy Holpin says that inband switch-based virtualisation raises concerns for many of his customers over performance and its ability to cope with future demands. Out-of-band, however, requires agents to be installed so is more rarely used, although EMC, for example, offers an out-of-band virtualisation appliance called InVista.
As well as pooling a set of arrays into a single resource, virtualisation can also provide a number of other capabilities, depending on the systems involved. “When you’ve 10 projects and want to allocate 1TB to each project, you can virtualise everything instead,” says NetApp’s consultant systems engineer, Dave Logan “You present your storage as 10TB when you only have 3-4TB at the back end, say, and then use a policy engine to expand volumes and delete snapshots accordingly.”
Virtualisation can also provide ILM capabilities using policy engines. By setting up rules for data importance, it’s possible for the virtualisation system to migrate data from tier 1 storage to tier 2 storage or archiving systems, while presenting the pooled storage as a single resource: the data will appear to be in the same location as before, but will actually be on a completely different and cheaper storage system. Alternatively, if an operator knows that certain data is accessed more frequently on certain days, it is possible to automatically move data between different tiers of storage to cope with the different levels of demand.
Of equal interest to many organisations is the possibility not just of getting more out of their existing storage but for seamless back-up to other systems using disk-to-disk replication. Instead of migrating data, the virtualisation system can copy data to other SANs or storage media while moving data on the primary SAN.
While all these technologies can bring additional business benefits to SANs, one of the bigger knock-on effects is in terms of savings – not in technology acquisition but management costs and staffing levels.
“There’s no question that for some customers, cost has been a big barrier to adoption,” says Dell’s enterprise marketing manager, Hugh Jenkins “We’ve been able to take cost down considerably over the last three years. But complexity has remained the big barrier.” By making storage easier to manage and automate, much of those costs can be reduced.
Storage virtualisation is by no means a panacea and implementing is far from simple. But when properly implemented, it provides a way for organisations not only to get more from what they’ve already got, but to make managing it simpler and more cost effective.
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