Log shipping
moves data from point A to point B relatively slowly. With data mirroring in High Protection
mode, all data transfer is synchronous. Any data modified at point A must first
be modified at point B. Some systems are more concerned about data loss than High
Availability??”that??™s where High Protection data mirroring comes in.
Failback
Since you have to destroy the database mirroring session completely if you want to bring
the mirror online, failback lets you reestablish the mirror session from the start. As with
High Performance mode, failback should have little or no impact on your clients, as long
as the name of the principal server has not changed.
nNote The database mirroring TCP ports are stored in the sys.database_mirroring_endpoints table.
They are disabled in the mirroring setup interface. When re-creating or reconfiguring the sessions in both
High Performance and High Protection modes, if you need to use different TCP ports, you??™ll need to remove
these entries from the endpoints table.
CHAPTER 8 n DATABASE MIRRORING 208
SYNCHRONOUS VS. ASYNCHRONOUS MIRRORING
Both High Protection and High Availability modes use synchronous communication, while High Performance
mode communicates asynchronously.
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