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How replication acceleration still saves SAN costs

23 Dec 13

Recent talk regarding WAN optimisation suggests that network optimisation features provided by SAN vendors are eliminating the need for replication acceleration.

At first glance, the position sounds compelling. Deduplication, compression and TCP optimisation, major features of WAN optimisation, are being bundled in many storage area networks (SANs).

So why bother with WAN optimisation?

The reality, though, is that most SAN platforms don’t include the ability to accelerate replication to remote SANs effectively. Many that offer features such as deduplication and compression are unable to apply them during data replication, where it’s needed most. Or where they are providing deduplication, they apply this feature at a block level that has low value in modern data environments with high rates of change.

I have seen replication acceleration eliminate over 75 per cent of the network bandwidth consumed by this already ‘deduplicated’ SAN data. The bandwidth savings result from a number of factors, but most notably the accelerator’s ability to deliver byte-level deduplication and wire speed compression to deliver the SAN’s data efficiently over the WAN.

And while almost every array allows IT specialists to modify the TCP window size and, in some cases, customise more advanced TCP options, arrays cannot deal with poor quality or shared networks. A large window size is fine until the network starts dropping packets or reordering packets to the extent that the receiving array thinks there is corrupted replication data.

In my experience with thousands of enterprise networks, they frequently suffer packet loss, particularly under the high load normally associated with replicating SAN data. When combined with any sort or latency, the resulting performance degradation can be catastrophic to Recovery Point Objectives (RPOs).

The traditional solution for this challenge was to provide dedicated high-grade links for SAN replication. However, with ballooning content and big data causing replication volumes to explode, this option is becoming too expensive for most organisations.

So unless SAN replication incorporates over the wire error or packet correction, an accelerator is required to address this issue and maintain RPO performance at a reasonable network price point.

So the current generation of replication acceleration is not just about deduplication, or window size, or even compression. It’s about the entire suite of enhancements that drive high performance and allows organisations to meet or exceed their RPOs at an affordable network cost.

If they cannot meet an RPO, or protect all the organisation’s data, or move that data over distance to assure its viability in the event of a local incident, it doesn’t matter if the data is deduplicated or optimised on the SAN. Seeing customers deploy replication acceleration in less than an hour and achieve performance figures that seemed impossible, is a very satisfying experience.

So I agree with testing WAN optimisation first before buying - because with the latest WAN acceleration software downloadable for free 30 day trial, organisations really should explore the potential.

By Brian Grant, Director Oceania, Silver Peak

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