EMC globalizes storage virtualization

NEW YORK, USA: The most far-reaching product unveiled at EMC World last week was storage hardware that allows multiple data centers to be federated into single virtual entities.

Called EMC vPlex, the product takes storage virtualization to a new level, and in time will further the use of public clouds.

Initially, vPlex will only link data centres that are relatively close to each other, but EMC promises that it will soon eliminate that distance limitation entirely, simplifying operations and increasing efficiency for multinational organizations.

Also Read: Caching in on cloud storage

vPlex pools resources across multiple data centres

A major benefit of server virtualization is that it allows applications to be moved from server to server while they are running. This enables on-the-fly load balancing across groups of servers, which improves overall efficiency.

It also increases application uptime by allowing applications to be moved without disruption when servers are taken offline for maintenance work.

Large customers would like to do this not only across groups of servers, but also across data centres. Without systems such as vPlex, the movement of virtual servers from one data centre to another is complicated by the need to also move the data they are working with.

vPlex eliminates this problem by making data simultaneously accessible in multiple locations.

Although vPlex has uses within single data centers, the ability to link multiple locations is its biggest virtue. Initially, vPlex will work only over distances of about 100km, which is enough to link data centers in the same metropolitan area.

EMC says it is already testing a version of vPlex that will work over global distances, and will ship it next year. Among the possibilities this will create is the movement of large batch-processing jobs between data centres to take advantage of day-to-night changes in energy prices.

vPlex will also allow smaller organizations to use virtual servers in public clouds without the problem of moving data to the service provider. This is a promise for the future because few production applications yet run in public clouds.

Other products that achieve the same result as vPlex include the FlexCache system already sold by EMC's arch-rival in storage, NetApp. EMC argues, however, that FlexCache and other products cannot handle the same volumes of data as vPlex, and are not as resilient.

vPlex will suit many but not all applications

Data needs to be kept in the same location as the virtual servers accessing it because of the latency introduced when data is accessed over distances.

This results from the speed of light, and from the latencies introduced by network gear itself. vPlex solves this problem by making caches or copies of data, and distributing the copies across multiple data centres.

Changes to the data then have to be propagated among the copies, and this activity itself introduces latencies. EMC says it has overcome this, and cites laboratory tests that show that vPlex inflicts only a minor overhead on application performance. vPlex will not suit high-speed financial trading systems, but according to EMC it will suit the majority of applications, including OLTP.

The latency effect will be increased for the long-distance versions of vPlex, which in storage terminology will have to work asynchronously. It is not clear how this will affect the number of applications that can work with vPlex over long distances.

EMC will not yet say, but suggests that applications could be modified to tolerate greater latencies, perhaps by extending time-out periods. There will certainly be limits on how much can be achieved this way, especially for transactional applications.

Server virtualization is currently dominated by VMware, and VMware is a subsidiary of EMC. But EMC is not restricting vPlex to work with VMware's software, and has qualified vPlex for use with virtual servers based on both VMware's vSphere and Microsoft's Hyper-V software.

This is not just because VMware's dominance of the virtualization market is set to dwindle over the next couple of years as Microsoft narrows the technical gap between itself and VMware in server virtualization. EMC also recognizes that large customers run systems from a mix of vendors, which is why vPlex will also work with data held on disk arrays sold by rivals such as IBM and Hitachi.

Source: Ovum