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The StorTrends® iTX WDS Implementation and Transfer Acceleration
Various remedies exist to counteract the irregularity of TCP over long distances; specific tunings
or accelerated protocols can sometimes be implemented to help alleviate this problem. Another
fairly common, though expensive, solution is to place pairs of dedicated appliances along the
transport path to boost or improve its throughput. As noted earlier, although the performance of
the TCP stack can be tweaked, it is a fairly accurate generalization that TCP is more suitable for
the LAN environment than it is in long-haul networks.
In iSCSI storage servers such as the StorTrends® 1U and 3U storage appliances from American
Megatrends, it is much more desirable to have the TCP stack optimized for the LAN environment.
This method of optimization is preferable since the server is 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. The figures below show the effect of packet loss and delays on long
distance replications using iSCSI, and the typical corresponding improvements achieved with
WDS in the Asynchronous Replication module found in StorTrends iTX:
Figure 2: Effect of Latency and Losses in TCP
WDS in StorTrends iTX: Compression and Data Deduplication for WAN
Asynchronous Replication
AMI offers these WDS features as an integral part of the StorTrends iTX stack, which can be
enabled or disabled through a robust feature licensing capability. Designed to provide the most
efficient and optimal asynchronous replication capability, WDS does so through powerful data
reduction (or data deduplication) and WAN acceleration features.
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StorTrends® 1300 User's Guide (StorTrends iTX version 2.7)
Figure 3: Effect of Latency and
Losses in StorTrends® Transfer
Protocol
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