Remote data replication over Wide Area Networks (WAN) has become increasingly widespread with the mass adoption and deployment of iSCSI-based storage appliances. However, despite its popularity, it is not without challenges.

One of the biggest challenges now facing replication over long distances is the delay incurred when doing so. Signals transported at nearly the speed of light are saddled with delays, resulting in latencies that can no longer be ignored, as is the case with WAN/LAN data transfers. These round-trip delays can range from a couple of milliseconds for inter-city connections to around 80-100 ms from coast-to-coast, and as much as 250-300 ms for submarine transmissions across the globe.

Since it is founded in iSCSI technology, StorTrends iTX Data Storage Software relies heavily on the TCP/IP protocol, optimized for LAN and SAN environments, for serving front-end I/Os and for synchronous replication operations. StorTrends iTX harnesses standards-based transport protocols to minimize the inefficiencies and high latencies of TCP/IP in WAN situations, and greatly improve and increase data transfer speed, approaching the theoretical maximum of the connection speed.

StorTrends iTX also provides additional performance gains through its WAN-optimization Data Services (WDS) module, which features data reduction technologies such as compression and data deduplication. Designed to provide the most efficient and optimal asynchronous replication capability, WDS does so through powerful data deduplication and WAN acceleration features.

In iSCSI storage servers such as the StorTrends 1U, 2U and 3U storage appliances from AMI, it preferable to have the TCP stack optimized for the LAN environment, since the servers used to serve I/Os over the iSCSI interconnect to the storage network (SAN), which is LAN-like in behavior. For replication over long distances, StorTrends iTX uses an intelligent combination of several standard IP transport protocols and a unique feature called WDS (WAN-optimization Data Services) to achieve near theoretical maximum throughput as determined by the bandwidth, taking into account the few resultant dropped packets.

Like many of its competitors, StorTrends employs delta-snapshot technology to transfer only the data that has changed between passes in order to reduce the amount of data transported. In addition to this, StorTrends also employs an intelligent data deduplication algorithm to filter out some of the previously transmitted data from earlier passes, in order to minimize the amount of data transported over WAN links.

In addition to the optimizations described above, StorTrends supports the compression and encryption of data before it is released on the WAN, which reduces the net size of data transferred over these more expensive links. StorTrends supports various compression depths, including an adaptive compression mode where the depth of compression is determined by an analysis of the current and statistical load on the system.

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