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Disaster recovery
21 Dell EMC SC Series: Microsoft Exchange Server Best Practices | CML1037
7 Disaster recovery
VSS snapshots can be replicated using the SC Series Remote Data Instant Replay. This would allow data (as
current as the last snapshot available) to be brought online at the main site or disaster recovery site.
If Exchange Server boots from SAN, snapshots from the boot volume and data volumes can be easily
mapped at the disaster recovery site, provided that duplicate hardware is used at the site. For the operating
system to boot properly, the volumes must be mapped to hardware that matches the original server hardware
at the main site. Additional steps for recovery beyond the scope of this document would have to be taken for
systems with dissimilar hardware at the main site and disaster recovery site.
It is important to understand the overall disaster recovery strategy around core services such as directory
services and DNS. Exchange relies heavily on Active Directory being available as well as DNS services.
Preparations must be taken to ensure that these dependencies are online and operational at the disaster
recovery site before the Exchange Server and its services can come online. Although Exchange data will be
available, it is equally important that the infrastructure is in place to allow for a smooth cutover, allowing users
to access Exchange soon after a disaster occurs.
7.1 Database copies and database availability groups
In the event of a hardware or software failure, multiple database copies in a database availability group (DAG)
enable high availability with fast failover and no data loss. This eliminates end-user downtime and lost
productivity that make up a significant cost of recovering from a past point-in-time backup to disk or tape.
DAGs can be extended to multiple sites and can provide resilience against data center failures as well.
While all Mailbox servers in a DAG must be in the same Active Directory domain, up to 16 copies of an
Exchange 2016/2019 mailbox database can be created on multiple mailbox servers, provided the servers are
grouped into a DAG. However, the round-trip network latency must not be greater than 250 milliseconds (ms).