Home > Storage > PowerFlex > White Papers > Microsoft SQL Server Data Protection using Dell PowerFlex Snapshots > PowerFlex snapshots and data consistency
PowerFlex snapshots support the notion of data consistency or consistency group by allowing snapshot creation of a group of volumes to take place as a unit, preserving write-order fidelity. When a snapshot operation takes place and includes a set of volumes, the snapshot is consistent across the participating volumes.
Consistent snapshots create a dataset that resembles the state of the application after a power failure, where databases such as SQL Server can simply restart from that state. For that reason, PowerFlex snapshots can be used to create database copies from running SQL Server databases. To make sure that the database can restart from that snapshot image, the snapshot must include all the volumes holding the database datafiles and transaction log files. This snapshot can then be mounted, and the SQL Server database can be opened. SQL Server database engine confirms that the datafiles and transaction logs are indeed consistent and opens the database as-of the time of the snapshot. Any outstanding committed transaction from the transaction log is rolled forwarded and reflected in the data, and any uncommitted transaction rolled back.
By themselves, consistent database snapshots are an efficient way to create the database copies. When the goal is to create valid SQL Server database backups, a coordination between the SQL Server and snapshot creation is required. This can be achieved by using a third-party software tool, such as AppSync that supports VSS or VDI backup APIs, or by using the new Microsoft SQL Server 2022 T-SQL Backup feature. When you follow the T-SQL storage snapshot feature, the target snapshot volumes can use the transaction log backups to roll forward database transaction to a time after the storage snapshot was created, such as expected from a backup solution.
Note that the PowerFlex snapshots are consistent across the set of volumes that participate in the operation. Once the snapshot operation is complete, PowerFlex does not force the notion of a group. That means that it is the responsibility of the user to continue to treat the volumes as a group for operations such as mounting them to a server, deleting them, creating additional snapshots from these volumes, and so on. To help the user with the notion of a group, a user-friendly alias can be provided while creating and restoring the snapshot. PowerFlex Manager also lists all the volumes that participated in a snapshot operation.
For more information about PowerFlex snapshots and how to use them, see the Dell PowerFlex: Snapshots Technical White Paper.