The Data Replication Bottleneck: Overcoming Out of Order and Lost Packets across the WAN

A Kubernan Brief

by Jim Metzler, Kubernan
Published November 2007, Posted November 2007



Many papers have been written on the effect that limited bandwidth and high latency have on application performance across the Wide Area Network (WAN). The purpose of this document is to address a less commonly understood WAN challenge that can also affect the performance of critical business applications - packet loss and reordering.

While packet loss and out of order packets are a nuisance for a network that supports typical data applications like file transfer and email, it is a very serious problem when performing data replication and backup across the WAN. The former involves thousands of short-lived sessions made up of a small number of packets typically sent over low bandwidth connections; the latter involves continuous sessions with many packets sent over high capacity WAN links. Data applications can typically recover from lost or out of order packets by retransmitting the lost data. Performance might suffer, but the results are not catastrophic. Data replication applications, however, do not have the same luxury. If packets are lost, throughput can be decreased so significantly that the replication process cannot be completed in a reasonable timeframe - if at all.

This paper will discuss why packet loss and ordering is becoming a bigger problem in today’s WANs, and what can be done to overcome these packet delivery challenges.

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