OpenMediaVault (OMV) is undoubtedly one of the finest dedicated operating systems for building a homemade NAS. It's not only completely free but also remarkably lightweight on hardware requirements. Built upon the solid foundation of Debian Linux, OMV comes equipped with all the essential features needed to get your NAS storage up and running. Furthermore, it offers the flexibility to add additional functionality through the use of plugins. All of this is presented in a modern and user-friendly interface.
OMV boasts compatibility with various file systems, including XFS, JFS, F2FS, Btrfs, Ext3, and most importantly, the highly efficient Ext4.