Microsoft® Exchange Server 2007 supports up to 50 databases per server that you can independently mount and dismount, and that you can organize into up to 50 storage groups. Microsoft Exchange Server 2010 includes support for up to 100 databases; this is because of the larger amount of memory that is available in the 64-bit platform, database engine performance improvements, and the reduced overhead that comes with the removal of storage groups.
Each Exchange 2010 database consists of a database file (*.edb), a transaction log stream (*.log), and a checkpoint file (*.chk). Transaction logs record all the changes that have been committed to the in-memory database, whereas checkpoint files record which logged transactions have been written to the on-disk database files. In Exchange 2010, log files are limited in size to 1 MB each .
Exchange 2010 maintains a single set of transaction log files for each database. The transaction logs play an important role in backup and recovery operations. You must handle these logs properly for a backup and recovery application that uses the Volume Shadow Copy Service (VSS) to be implemented correctly.
On each Exchange 2010 server, you can mount no more than one database at a time as a recovery database and accessed by means of Windows® PowerShell® commands such as Restore-Mailbox.
Exchange 2010 introduces the concept of database mobility, in which you can replicate each database on a maximum of 15 other Exchange servers. For more information about database mobility and database availability groups (DAGs), see Exchange Database Mobility.