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BP1013 Best Practices for Enhancing Microsoft Exchange Server 2010 Data Protection and Availability 39
Figure 17 shows the data flow for a DAG reseeding process using a Smart Copy on the iSCSI SAN.
Figure 17 DAG seeding process data flow when reseeding from a preexisting Smart Copy snapshot
We compared the time taken to restore the data redundancy of one database across the two
Exchange DAG nodes in case of loss of the secondary copy (corruption, deletion, etc.).
• In the first case we measured the time taken for seeding over the network with the native
Exchange Replication mechanism
• In the second case we restored a Smart Copy snapshot from the SAN on the second node and
then resumed the database replication in order to re-sync the database delta from the time
the snapshot was taken to the current time at the primary database copy
We simulated the loss of the redundant database copy after 50 minutes from the last snapshot, so we
then had around 1100 outstanding logs generated on the source node ready to be copied to the
second node and replayed to the database copy. As shown in Table 8, our test took 243 minutes for
Exchange reseeding over the replication network, however, when assisted by EqualLogic Smart Copy
snapshot, the time taken to reseed was only about 15 minutes. This clearly shows the benefit of using
snapshots to improve the time it takes to bring back the availability level of a DAG.