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In terms of the number of databases supported in Microsoft Exchange 2000 Server versus what is available in Exchange Server 5.5, Exchange 2000 supports substantially more.
The recommendation for database capacity planning on non-clustered Exchange 2000 Servers is a maximum of four storage groups that contain a maximum of five databases for each storage group. This results in a maximum of 20 databases for each Exchange 2000 server.
This limit is enforced inside the Exchange System Manger snap-in, so administrators cannot create more storage groups than the system enables.
For backup and recovery, Exchange 2000 enables one active backup or restoration of a database for each storage group at any one time.
These new values affect the deployment of cluster servers. For example, in a sample configuration of a two-node cluster with two storage groups for each node (assigned to virtual servers), if failover occurs, one node may have four storage groups.
The fundamental rule is that a single server cannot host more than four storage groups at any one time.
Exchange 2000 enables an administrator to perform exactly one simultaneous backup for each storage group. Therefore, the maximum number of parallel backups equals the number of configured storage groups. Therefore, if you have four storage groups, you can have up to four parallel backups going on, but each backup must be focused on a different storage group.
As the four-storage group limit is enforced in Exchange System Manger rather than in the Extensible Storage Engine (ESE) code itself, the value of 16 storage groups remains. This means, theoretically, that the maximum number of parallel restores is limited by the number of active storage groups.