The Stortrends Itx Wds Implementation And Transfer Acceleration; Figure 3: Effect Of Latency And Losses In Tcp; Figure 4: Effect Of Latency And Losses In Stortrends Transfer Protocol - American Megatrends StorTrends 2200 User Manual

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 StorTrends 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 3: Effect of Latency and Losses in TCP

Figure 4: Effect of Latency and Losses in StorTrends Transfer Protocol

258 StorTrends/ManageTrends (version 2.7) Web Interface User's Guide for the StorTrends 2200 Storage Appliance