What is an application consistent backup?
Applications like Microsoft SQL Server and Microsoft Exchange are database applications and typically write application memory to log files before the contents are committed to the database. When the application data is backed up, it is important that the contents of the memory and any pending writes are completed and captured in the backup. If the contents of memory are not allowed to flush to disk, the state of the backup is equivalent to that of a power plug being pulled off the server. When the server is recovered from a backup which did not allow the pending I/O operations to complete, the database will have to follow procedures to replay or integrate logs to the database files. So an application-consistent backup is one that informs the application that a backup is about to take place and allows the application to achieve a quiescent and consistent state by flushing any pending I/O operations to disk.
How are application-consistent backups achieved?
Volume Shadow Copy Service (VSS) is a framework designed primarily to address this problem. It is a backup infrastructure which allows a backup application to create application-consistent backups. When a backup is initiated, VSS performs a Copy-On-Write (COW) operation on the volume, but before doing so, it informs every application that it needs to flush its memory-resident data to disk. VSS then allows the backup application to read the snapshot data to send it to secondary and tertiary storage. In the case of an application running inside a virtual machine on Hyper-V, a VSS aware backup of the Hyper-V host, leveraging Hyper-V Integration Services, communicates with the VSS writers in the guest virtual machine to perform an application-consistent backup of the virtual machine and the application it houses. Unitrends protects Hyper-V virtual machines by integrating with the VSS framework to perform application-consistent backups.
But I have more granular needs to protect the applications …
- I want to protect the databases with a different backup strategy than the virtual machine itself.
- To comply with corporate policy, I am required to have a stricter RPO than the virtual machine itself
- I would like to backup and protect just a subset of the total databases in the virtual machine.
- I would like the ability to recover an individual database to a particular minute and roll the transaction logs right before my database geo corrupted.
- I would like to select which database datasets should be copied to rotational archiving media for long term retention. I want different long term retention policies for various databases I protect
- I want to replicate only a few databases offsite, not all.
If you answered yes to one or more of the questions above, you need a solution that can not only offer the simplicity of a application-consistent host based virtual machine backup, but also provide the enterprise features to protect the application data to meet your data protection requirements. Unitrends’ Simply Scalable architecture is designed to offer this level of application control while keeping simplicity in the forefront.