Microsoft SQL Server 2022 is now available in public preview, and it’s jam-packed with great new features. One of the most exciting is the Transact-SQL snapshot backup feature. This is a gem that can transform your backup and recovery strategy and turbocharge your database recoveries!

The power of snapshots

At Dell Technologies we have known the power of storage snapshots for over a decade. Storage snapshots are a fundamental feature in Dell PowerStore and the rest of the Dell storage portfolio. They are a powerful feature that allows point-in-time volume copies to be created and recovered in seconds or less, regardless of size. Since the storage is performing the work, there is no overhead of copying data to another device or location. This metadata operation performed on the storage is not only fast, but it’s space-efficient as well. Instead of storing a full backup copy, only the delta is stored and then coalesced with the base image to form a point-in-time copy.

Starting with SQL Server 2019, SQL Server is also supported on Linux and container platforms such as Kubernetes, in addition to Windows. Kubernetes recognized and embraced the power of storage-based snapshots and provided support a couple of years ago. For managing large datasets in a fast, efficient manner, they are tough to beat.

Lacking full SQL Server support

Unfortunately, prior to SQL Server 2022, there were limitations around how storage-based snapshots could be used for database recovery. Before SQL Server 2022, there was no supported method to apply transaction log backups to these copies without writing custom SQL Server Virtual Device Interface (VDI) code. This limited storage snapshot usage for most customers that use transaction log backups as part of their recovery strategy. Therefore, the most common use cases were repurposing database copies for reporting and test/dev use cases.

In addition, in SQL Server versions earlier than SQL Server 2022, the Volume Shadow Copy Service (VSS) technology used to take these backups is only provided on Windows. Linux and container-based deployments are not supported.

SQL Server 2022 solves the problem!

The Transact-SQL (T-SQL) snapshot backup feature of SQL Server 2022 solves these problems and allows storage snapshots to be a first-class citizen for SQL Server backup and recovery.

There are new options added to T-SQL ALTER DATABASE, BACKUP, and RESTORE commands that allow either a single user database or all user databases to be suspended, allowing the opportunity for storage snapshots to be taken without requiring VSS. Now there is one method that is supported on all SQL Server 2022 platforms.

T-SQL snapshot backups are supported with full recovery scenarios. They can be used as the basis for all common recovery scenarios, such as applying differential and log backups. They can also be used to seed availability groups for fast availability group recovery.

Time to rethink

SQL Server databases can be very large and have stringent recovery time objectives (RTOs) and recovery point objectives (RPOs). PowerStore snapshots can be taken and restored in seconds, where traditional database backup and recovery can take hours. Now that they are fully supported in common recovery scenarios, T-SQL snapshot backup and PowerStore snapshots can be used as a first line of defense in performing database recovery and accelerating the process from hours to seconds. For Dell storage customers, many of the Dell storage products you own support this capability today since there is no VSS provider or storage driver required. Backup and recovery operations can be completely automated using Dell storage command line utilities and REST API integration.

For example, the Dell PowerStore CLI utility (PSTCLI) allows powerful scripting of PowerStore storage operations such as snapshot backup and recovery.

Storage-based snapshots are not meant to replace all traditional database backups. Off-appliance and/or offsite backups are still a best practice for full data protection. However, most backup and restore activities do not require off-appliance or offsite backups, and this is where time and space efficiencies come in. Storage-based snapshots accelerate the majority of backup and recovery scenarios without affecting traditional database backups.

A quick PowerStore example

Backup

The overall workflow for a T-SQL snapshot backup is:

1. Issue the T-SQL ALTER DATABASE command to suspend the database:
   ALTER DATABASE SnapTest SET SUSPEND_FOR_SNAPSHOT_BACKUP = ON
   
   
2. Perform storage snapshot operations. For PowerStore, this is a single command:
   pstcli -d MyPowerStoreMgmtAddress -u UserName -p Password volume_group -name SQLDemo -name SnapTest-Snapshot-2208290922 -description “s:\sql\SnapTest_SQLBackupFull.bkm”
   
   
3. Issue the T-SQL command BACKUP DATABASE command with the METADATA_ONLY option to record the metadata and resume the database:
   BACKUP DATABASE SnapTest TO DISK = 's:\sql\SnapTest_SQLBackupFull.bkm' WITH METADATA_ONLY,COPY_ONLY,NOFORMAT,MEDIANAME='Dell PowerStore PS-13',MEDIADESCRIPTION='volume group: SQLDemo',NAME='SnapTest-Snapshot-2208290922',DESCRIPTION=' f85f5a13-d820-4e56-9b9c-a3668d3d7e5e ' ;

Since Microsoft has fully documented the SQL Server backup and restore operations, let’s focus on step 2 above, the PowerStore CLI command. It is important to understand that when taking a PowerStore storage snapshot, the snapshot is being taken at the volume level. Therefore, all volumes that contain data and log files for your database require a consistent point-in-time snapshot. It is a SQL Server Best Practice for PowerStore to place associated SQL Server data and log volumes into a PowerStore volume group. This allows for simplified protection and consistency across all volumes in the volume group. In the PSTCLI command above, a PowerStore snapshot is taken on a volume group containing all the volumes for the database at once.

Also, a couple of tips for making the process a bit easier. The PowerStore snapshot and the backup metadata file need to be used as a set. The proper version is required for each because the metadata file contains information such as SQL Server log sequence numbers (LSNs) that need to match the database files. Therefore, I’m using several fields in the PowerStore and SQL Server snapshot commands to store information on how to tie this information together:

• When the PowerStore snapshot is taken in step 2 above, in the name field I store the database name and the datetime that the snapshot was taken. I store the path to the SQL Server metadata file in the description field. 

• In step 3, within the BACKUP DATABASE command, I put the PowerStore friendly name in the MEDIANAME field, the PowerStore volume group name in the NAME field, and the PowerStore volume group ID in the DESCRIPTION field. This populates the metadata file with the necessary information to locate the PowerStore snapshot on the PowerStore appliance.
  
  
• The T-SQL command RESTORE HEADERONLY will display the information added to the BACKUP DATABASE command as well as the SQL Server name and database name.

Recovery

The overall workflow for a basic recovery is:

1. Drop the existing database.
   
   
2. Offline the database volumes. This can be done through PowerShell, as follows, where X is the drive letter of the volume to take offline:
   Set-Disk (Get-Partition -DriveLetter X | Get-Disk | Select number -ExpandProperty number) -isOffline $true
   
   
3. Restore the database snapshot using PowerStore PSTCLI:
   
   
   1. List volume groups.
      pstcli -d MyPowerStoreMgmtAddress -u UserName -p Password! volume_group show
      
      
   2. Restore the volume group where f85f5a13-d820-4e56-9b9c-a3668d3d7e5e is a volume group ID from above.
      pstcli -d MyPowerStoreMgmtAddress -u UserName -p Password! volume_group -name SQLServerVolumeGroup restore -from_snap_id   f85f5a13-d820-4e56-9b9c-a3668d3d7e5e 
      
      
4. Online the database volumes. The following PowerShell command will online all offline disks:
   Get-Disk | Where-Object IsOffline -Eq $True | Select Number | Set-Disk -isOffline $False
   
   
5. Issue the T-SQL RESTORE DATABASE command referencing the backup metadata file, using the NORECOVERY option if applying log backups:
   RESTORE DATABASE SnapTest FROM DISK = 's:\sql\SnapTest_PowerStore_PS13_SQLBackup.bkm' WITH FILE=1,METADATA_ONLY,NORECOVERY
   
   
6. If applicable, apply database log backups:
   RESTORE LOG SnapTest FROM DISK = 's:\sql\SnapTest20220829031756.trn' WITH RECOVERY

Other items of note

A couple of other items worth discussing are COPY_ONLY and differential backups. You might have noticed above that the BACKUP DATABASE command contains the COPY_ONLY parameter, which means that these backups won’t interfere with another backup and recovery process that you might have in place.

It also means that you can’t apply differential backups to these T-SQL snapshot backups. I’m not sure why one would want to do that; I would just take another T-SQL snapshot backup with PowerStore at the same time, use that for the recovery base, and expedite the process! I’m sure there are valid reasons for wanting to do that, and, if so, you don’t need to use the COPY_ONLY option. Just be aware that you might be affecting other backup and restore operations, so be sure to do your homework first!

Stay tuned

There will be a lot more information and examples coming from Dell Technologies on how to integrate this new T-SQL snapshot backup feature with Linux and Kubernetes on PowerStore as well as on other Dell storage platforms. Also, look for the Dell Technologies sessions at PASS Data Community Summit 2022, where we will have more information on this and other exciting new Microsoft SQL Server 2022 features!

Author: Doug Bernhardt
Sr. Principal Engineering Technologist
https://www.linkedin.com/in/doug-bernhardt-data/