File Backup and Restore and Compression
Microsoft SQL Server supports NTFS file system data compression of read-only filegroups and read-only databases. For more information, see Read-Only Filegroups and Compression.
Restoring files in a read-only filegroup is supported on compressed NTFS files. Backup and restore of these filegroups works essentially as it would for any read-only filegroup, with the following exceptions:
Restoring a read-write file (including the primary or log files of a read-write database) to a compressed volume fails and displays an error.
Restoring a read-only database to a compressed volume is allowed.
Log files of read/write databases should never be placed on compressed file systems.