Technology NAS
around the world. As a result, they are often unnecessarily “chatty,” meaning that they expect to carry on a rapid-fire conversation between client and server whenever they transmit a block of data. That is fine when each transmission and acknowledgement takes milliseconds on a LAN, but it becomes a problem when each of these exchanges is stretched over a longer connection and the delays start to add up.
One way around this is to deploy an optimisation appliance at either end of the WAN connection, which can transparently streamline these file transfer conversations and minimize the effect of network delays. The best of these devices can eliminate in the range of 65 to 98% of network round trips.
Look for products that support a wide range of network file system and replication protocols, including those associated with specific network storage products. For example, users of EMC’s Symmetrix V-MAX and DMX storage systems will want support for SRDF/A. This is EMC’s protocol for asynchronous file replication, often used for replication between data centres or to disaster recovery facilities.
Along with protocol streamlining, WAN optimisation devices dramatically reduce the amount of data that must be transmitted, which both speeds transmission and lessons the load on the network. The bandwidth required to transmit a file can often be reduced by 60 to 95%.
This is achieved with a combination of compression and data deduplication techniques. For example, suppose you are backing up a directory of word processing documents that includes multiple drafts of the same press release. Your WAN appliance
can identify when a block of data is identical to one that it has already transmitted. In those cases, instead of transmitting the data itself, it sends a reference that the appliance on the other end of the connection can use to retrieve that data from its cache. So if each draft of a document is 95% the same as the last, with WAN optimisation you only need to stream the fraction that has changed across the network.
Further, even different documents might all contain a section that is always the same, which would only have to be transmitted once for many documents. At the same time, the data that is not duplicated can still be compacted – often by a factor of 100 – using standard file compression algorithms like Lempel-Ziv (LZ).
In combination, these protocol and deduplication optimisations often allow a single file to be copied across the WAN more than 250 times faster than would be possible to without optimisation. An entire directory of files can be copied nearly 20 times faster, while lowering the bandwidth required by up to 98%.
The payoff from these improvements comes every time a branch office employee downloads a procedures manual from the corporate data centre, or a factory scheduling application retrieves the latest sales demand projections from headquarters. If a critical enterprise server crashes and must be restored from backups stored offsite, WAN optimisation will pay off in spaces by allowing you to retrieve that backup data many times quicker – and get back in business.
All these things are possible, for those who plan their network and storage strategies properly.
WWW.SNSEUROPE.COM FEBRUARY | 2011 31
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