For Microsoft SQL, Exchange, Active Directory and SharePoint, Veeam Backup & Replication™ creates application-consistent, image-level backups by leveraging VSS, ensuring successful recovery of business-critical applications and services and allowing for application-specific restore scenarios.
According to Microsoft limitations, applications cannot be kept frozen longer than for 60 seconds (20 seconds for Microsoft Exchange). If the Microsoft VSS writer keeps application data frozen longer than this period, a VSS processing timeout occurs, and Veeam Backup & Replication fails to create a transaction-consistent backup of the VM. The VSS processing timeout is a common problem for highly transactional applications such as Microsoft Exchange.
To overcome this limitation, Veeam Backup & Replication uses the persistent VSS snapshots technology for backup of Microsoft Exchange VMs. If Microsoft Exchange must be kept frozen for a longer period than the allowed one, Veeam Backup & Replication automatically fails over to the persistent VSS snapshot mechanism.