Home > Storage > Unity XT > Virtualization, Cloud & Applications > Dell Unity XT: Microsoft SQL Server Best Practices > File-level retention and SQL Ledger
With SQL Server 2022, Microsoft introduced a feature called Ledger that allows database tables to be examined for tampering. This functionality is based on blockchain technology and creates a ledger table of data hash values that are stored in a blockchain. This ledger digest and its verification can be stored on a write once read many (WORM) storage device. This allows organizations to comply with data storage requirements such as SEC rule 17a-4(f) which address unauthorized data tampering and/or data deletion.
The Unity XT File-level retention (FLR) feature allows a WORM storage device to be created by creating a Unity XT file system and then setting the file-level retention. There are two levels of file-level retention with this feature, Enterprise (FLR-E) and Compliance (FLR-C). Essentially FLR-E prevents data changes from users and storage administrators to individual files, but the storage administrator can delete the entire file system. FLR-C prevents all deletion, including deletion of the file system.
To create a Unity XT file system to be used as a WORM device, enable FLR, select Enterprise or Compliance, and then leave the default and maximum retention period set to Unlimited.
Once the file system is in place, digests for Ledger tables can be created and stored on the Unity XT file system with File-level retention enabled.
The following article talks about how to configure digest storage for on-premises WORM storage such as Unity XT: https://techcommunity.microsoft.com/t5/sql-server-blog/ledger-automatic-digest-upload-for-sql-server-without-azure/ba-p/3630992
For more information about Unity XT FLR, refer to the Unity File-Level Retention paper.