Backing up mailboxes requires careful planning. The following sections provide some considerations for Volume Shadow Copy Service (VSS) and streaming online backups.

There are trade-offs in every solution that affect variables such as cost, time, and reliability. Most administrators define a time for online database maintenance, defragmentation, and operating system maintenance. These activities compete with the backup time. Special care is needed to balance backup, maintenance, and production load. Larger mailboxes may make a daily full backup strategy impossible to complete within your Service Level Agreement (SLA).

A common strategy to lessen the impact of a full nightly backup is to perform weekly full backups and daily differential backups. With this strategy, you need to recover the full backup, and then recover the last differential backup.

Although VSS backups can be made on either the production or copy data, we recommend that you back up the copy and avoid an impact to the production physical disks.

With local continuous replication (LCR), Exchange Server 2007 is replicating transaction logs to a separate disk on the same server. When using VSS clones on the copy, the copy storage should be configured on different physical disks so that the clone operation and checksum integrity do not affect the production physical disks. With VSS snapshots on the copy, the copy storage should be configured on different physical disks so that the checksum integrity and subsequent streaming to tape do not affect your production physical disks.

With cluster continuous replication (CCR), Exchange Server 2007 is replicating transaction logs to a separate server. This server is a node in the cluster, but the target copy is not kept on shared storage. When using VSS clones, you can run the checksum integrity on the copy on the passive node by using different physical disks, thereby isolating the backup process. With VSS snapshots, the checksum integrity and subsequent streaming to tape will not impact your production server or physical disks.

Unlike hardware-based VSS backups, where the data is typically moved within the storage appliance, when using streaming backups, the server is responsible for moving your data. The performance impact of the checksum integrity process is not an issue because every page is checked during the backup. In the case of concurrent backups, multiple streams can stress the limits of your backup media, whether it is gigabit Ethernet or fiber channel attached tape. For many customers, the backup SLA window, divided by the throughput-per-minute of their streaming backup medium, limits the permissible size of the storage group. For example, if you had a one-hour SLA on your storage group, and can back up 100 megabytes (MB) per second, your maximum storage group size would be 360 gigabytes (GB).