File-level retention (FLR) is an EMC® VNX™ series software feature for protecting files from modification or deletion until a specified retention date. By using file-level retention, you can archive data to FLR storage on standard rewritable magnetic disks through NFS or CIFS operations. FLR allows you to create a permanent, unalterable set of files and directories and ensure the integrity of data.

To get more information about this technology please read through the following document:

Using VNX File-Level Retention 7.0