Concurrent bulk transfers can occur over the WAN. Under normal operations, setting the number of concurrent bulk transfers between two sites to 1 is sufficient because bulk transfers are relatively uncommon. In case of a site/WAN outage, this limit can result in long recovery times.
Configuring the Concurrent Bulk Transfers setting specifies the number of servers that simultaneously perform a bulk transfer across the WAN. A bulk transfer can happen when a server starts COMCOL or is demoted from active status. A bulk transfer copies one or more database tables to the secondary site database because the record of database updates is not available. Unlike steady-state replication, which is limited by the rate of updates applied to the database, bulk transfer sends the table as fast as possible.
The recommended number is based on the available bandwidth within the WAN. For example, if the WAN transfer speed is 1GB/s, set Concurrent Bulk Transfers to 1 .