Determining the Interval

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Applies To: Windows Server 2003, Windows Server 2003 R2, Windows Server 2003 with SP1, Windows Server 2003 with SP2

You must set the site link replication interval property to indicate how frequently you want replication to occur during the times when the schedule allows replication. For example, if the schedule allows replication between 02:00 hours and 04:00 hours, and the replication interval is set for 30 minutes, replication can occur up to four times during the scheduled time. The default replication interval is 180 minutes, or 3 hours.

Consider the following criteria to determine how often replication occurs within the schedule window:

  • A small interval decreases latency but increases the amount of WAN traffic.

  • To keep domain directory partitions up to date, low latency is preferred.

With a store-and-forward replication strategy, determining just how long a directory update might take to be replicated to every domain controller is difficult. To provide a conservative estimate of maximum latency, perform these tasks:

  • Create a table of all the sites on your network, as shown in Table 3.3.

    Table 3.3   Maximum Latency (in Hours) of Replication Between Sites

      Seattle Boston Los Angeles New York Washington DC

    Seattle

    0.25

    		        

    Boston

    		  

    0.25

    		      

    Los Angeles

    		    

    0.25

    		    

    New York

    		      

    0.25

    		  

    Washington DC

    		        

    0.25

    An average, worst-case latency within a site is estimated to be 15 minutes.

  • From the replication schedule, determine the maximum replication latency possible on any site link connecting two hub sites.

    For example, if replication occurs between Seattle and New York every three hours, then the maximum delay for replication between these sites is 3 hours. If the replication delay between New York and Seattle is the longest scheduled delay among all hub sites, then the maximum latency between all hubs is 3 hours.

  • For each hub site, create a table of the maximum latencies between the hub site and any of its satellite sites.

    For example, if replication occurs between New York and Washington, DC, every four hours and this is the longest replication delay between New York and any of its satellite sites, then the maximum latency between New York and its satellites is four hours.

  • Combine these maximum latencies to determine the maximum latency for the entire network.

    For example, if the maximum latency between Seattle and its satellite site in Los Angeles is one day, the maximum replication latency for this set of links (Washington, DC-New York-Seattle-Los Angeles) is 31 hours (4 (Washington, DC-New York)+ 3 (New York-Seattle) + 24 (Seattle-Los Angeles)) as shown in Table 3.4.

    Table 3.4   Maximum Latency (in Hours) of Replication Between Sites

      Seattle Boston Los Angeles New York Washington DC

    Seattle

    0.25

    4+3

    24.00

    3.00

    4+3

    Boston

    		  

    0.25

    4+3+24

    4.00

    4.00

    Los Angeles

    		    

    0.25

    24 + 3

    24+3+4

    New York

    		      

    0.25

    4.00

    Washington, DC

    		        

    0.25

Review your maximum replication latency, and revise your replication schedule and interval if necessary.