How does automatic seeding work in SQL Server 2016?
SQL Server 2016 introduces a new feature to initialize a secondary replica – automatic seeding. Automatic seeding uses the log stream transport to stream the backup using VDI to the secondary replica for each database of the availability group using the configured endpoints.
Why is automatic seeding slower for Secondary replicas?
In practice, the automatic seeding process is slower, as network signals degrade over longer distances and the link is shared with other resources on the network. During seeding, the transaction log on the database at the primary replica continues to grow and cannot be truncated until automatic seeding of that database is complete.
How is a secondary replica seeded in SQL Server?
This secondary replica is seeded from the primary of the second availability group. Automatic seeding may or may not be practical to initialize a secondary replica, depending on the size of the database, network speed, and distance between the primary and secondary replicas.
Do you have to backup database before auto seeding?
With this capability enabled you do not have to manually backup and restore the database and transaction logs before starting data synchronization with the primary replica. Databases must be in Full recovery model and at least one Full backup must have been taken of the database (to start the recovery chain)
How to use compression during automatic seeding in SQL Server?
To use compression during automatic seeding, enable trace flag 9567 – see Tune compression for availability group. In SQL Server 2016 and before, the folder where the database is created by automatic seeding must already exist and be the same as the path on the primary replica.
How to initialize a database using automatic seeding?
On the secondary instance SQL Server uses one thread per LUN to initialize database. Set trace flag 9567 on the primary replica to enable compression of the data stream during automatic seeding. This can significantly reduce the transfer time of automatic seeding, however it also increases the CPU usage.
How many databases can automatic seeding be used for?
Automatic seeding is a single-threaded process that can handle up to five databases. The single-threading affects performance, especially if the availability group has more than one database. Compression can be used for automatic seeding, but it is disabled by default.