4.15 of the faq says Unfortunately, there are no known disk imaging packages which are FFS-aware.
I haven't tested whether a broad brush had been applied expecting ufs and ffs to be the same or if clonezillas statement is correct but thought it may be worth bringing up that clonezilla.org says Filesystem supported: (1) ext2, ext3, ext4, reiserfs, reiser4, xfs, jfs, btrfs of GNU/Linux, (2) FAT12, FAT16, FAT32, NTFS of MS Windows, (3) HFS+ of Mac OS, (4) UFS of FreeBSD, NetBSD, and OpenBSD, and (5) VMFS3 and VMFS5 of VMWare ESX. Therefore you can clone GNU/Linux, MS windows, Intel-based Mac OS, and FreeBSD, NetBSD, and OpenBSD, no matter it's 32-bit (x86) or 64-bit (x86-64) OS. For these file systems, only used blocks in partition are saved and restored. For unsupported file system, sector-to-sector copy is done by dd in Clonezilla.
