Microsoft has made great improvements in Exchange 2013, some of these around Database Availability Groups [DAGs]. For example, it is now possible to reseed a database from multiple sources, greatly reducing the overall time this operation usually takes. Another improvement, in this case a new feature, is called Automatic Reseed, or simply AutoReseed.
With Exchange 2010, if you lose the disk where your database is (either active or passive), Exchange will failover that database to another server (assuming it is part of a DAG with multiple copies). After that, an administrator will typically replace the faulted disk and reseed the database back to that server. This, of course, in scenarios where resilience through RAID or enterprise-level storage is not provided, which would cater for disk failures.
The purpose of AutoReseed is to overcome this situation and automatically restore database redundancy by using spare disks provisioned specifically for this. All it involves is pre-mapping volumes and databases using mount points that will be used for the databases and the reseed operation. In a simplistic way:
- Mount all volumes (used for databases and as spares) under a single mount point, C:\ExchangeVolumes for example;
- Mount the root directory of mailbox databases as another mount point under C:\ExchangeDatabases for example. Next, create two directories for each database: one for the database itself and another for the log files;
- Finally create the database(s).
Here is AutoReseed process flow:
- The Exchange Replication service periodically scans for database copies that have a status of FailedAndSuspended;
- If one is found, it does pre-requisite checks like checking if spare drives are available and ensuring nothing might prevent Exchange from automatic reseeding the database;
- If all the checks pass, the Replication service allocates and remaps a spare drive;
- Seeding is performed;
- Once seeding is complete, the Replication service checks if the seeded copy is healthy.
All an administrator needs to do now is simply replace the faulty disk and reconfigure it as a spare for the DAG!
To read all about this new feature and how to implement it, please check the article at MSExchange.org.