Shrinking the size of a volume on a SQL Server

Question

Hello.

We need to shrink the size of a Windows volume from its current sixty-five, 65, terabytes to sixty, 60, terabytes. The reason for this move is due to the Microsoft Volume Shadow Service, VSS, having an operational limit of sixty-four, 64, terabytes for a given volume. The VSS is used with our cloud backup service.

The server operating system is Windows 2019 Standard running the SQL 2016 Standard database. The volume is a simple type running on an iSCSI basic disk. The data that is on the volume is the FILESTREAM folders for multiple databases. There is eighteen, 18, terabytes of available space on the volume, and the goal is to reduce the volume by five, 5, terabytes in order to have the cloud backup, Rubrik, be able to complete the backups of the respective databases.

The plan is to go into Disk Management snap-in and select the 'Shrink Volume' option. Prior to doing so, I am going to be stopping all SQL services. Is there anything else that I need to consider or do before proceeding?

Answer 1

Yep - this is a supported Windows operation. The fact that the volume contains SQL Server FILESTREAM data should not play a role here. Stopping the SQL Server services that use the FILESTREAM containers is the correct precaution so that SQL Server is not actively accessing the volume during the operation.

Before proceeding, verify that you have a recent successful backup of the affected databases and FILESTREAM data. Then confirm the volume is NTFS, is the expected basic-disk volume, and that no other applications are actively using it. In addition, check the actual shrinkable space before attempting the 5 TB reduction. The 18 TB of free space does not necessarily mean that 18 TB can be removed. Run:

diskpart
list volume
select volume <volume-number>
shrink querymax

If Windows reports at least 5 TB as available to shrink, you can proceed. You can then use Disk Management → right-click the volume → Shrink Volume, and specify the 5 TB reduction. Windows will relocate movable NTFS data as necessary - you do not need to manually move the FILESTREAM files or reformat the volume.

You shouldn't reduce the underlying iSCSI LUN first - instead shrink the Windows volume/partition first. If you subsequently want to reduce the physical iSCSI LUN to reclaim the unused 5 TB, that is a separate storage operation.

Afterward, verify that the volume is approximately 60 TB, start SQL Server, confirm that all FILESTREAM databases come online normally, and then perform a backup test. The successful backup is the final confirmation that the volume-size issue has been resolved.

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hth

Marcin

Answer 2

Yes. The supported Windows-side considerations are:

1. Confirm the volume is eligible for shrink
   • A volume can be shrunk only if it has no file system or uses NTFS.
   • The DiskPart shrink command works on basic volumes and on simple or spanned dynamic volumes, but not on OEM, EFI, or recovery partitions.
2. Use an account with the required rights
   • Membership in Backup Operators or Administrators is required.
3. Understand what shrink actually does
   • Shrinking reduces the partition into adjacent, contiguous space on the same disk.
   • Ordinary files are automatically relocated on the disk to create the new unallocated space.
   • The disk does not need to be reformatted.
4. Be aware that some files can block the operation
   • Certain file types can prevent or limit shrinking.
   • Before making the change, check the maximum reclaimable amount with DiskPart:

          diskpart
          list volume
          select volume <volume-number>
          shrink querymax
     

   • This shows the maximum number of MB that can currently be reduced.
5. Proceed through Disk Management or DiskPart
   • In Disk Management: right-click the volume and select Shrink Volume, then follow the wizard.
   • In DiskPart:

          diskpart
          list volume
          select volume <volume-number>
          shrink desired=<size-in-MB> minimum=<size-in-MB>
     

   • Example syntax from Microsoft:

          shrink desired=500 minimum=250
     

6. Watch for data risk on raw partitions
   • If the partition is a raw partition that contains data, shrinking it can destroy that data.
   • This caution does not apply to an NTFS volume in the same way, but it is an important boundary condition.
7. Volume size planning consideration
   • Microsoft guidance for clustered Azure Local and Windows Server environments recommends limiting each volume to 64 TB.

The context does not provide any SQL Server-specific requirement beyond the Windows volume-shrink behavior, so only the supported Windows considerations above can be stated.

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• Shrink a basic volume
• shrink
• Plan volumes on Azure Local and Windows Server clusters
• Volume Shadow Copy Service (VSS)