Public folder replication is tricky even at the best of times. Few Exchange administrators understand how and when replication occurs, and the Exchange administrative tools, especially Exchange System Manager (ESM), are weak in this area, perhaps because Microsoft knew that it would eventually move away from public folders. When public folder replication gets out of hand, a phenomenon called a replication storm can occur. Public folder replication storms happen when an uncontrolled or unexpected amount of replication activity is generated within the organization, so that network links are swamped with data being exchanged between public folder servers to update their folder replicas. You can take control of replication storms, however, thanks to the Public Folder Content Replication feature, a small but significant feature that Microsoft slipped into Exchange Server 2003 Service Pack 2 (SP2).
Difficult to Diagnose
A replication storm is typically caused by a change that an administrator makes,
although bugs in pre-Exchange 2000 Server SP2 versions have been known to cause
replication storms, too. Sometimes a storm is the result of planned activity,
such as when you add a new public folder server to the organization and need
to replicate a large amount of data to that server to populate the set of folder
replicas. You can plan ahead by implementing such changes when network activity
is minimal (such as after hours or over a weekend). That way, the extra replication
traffic won't interfere with regular business, and the storm should finish by
the time users get to work. . . .
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