For general use, the knowledge base recommends Btrfs in most scenarios.
Btrfs
It is described as suitable for:
- Storing critical business data that require data integrity and protection
- General file sharing or providing iSCSI LUNs for server virtualization
The knowledge base also notes that on a Btrfs volume, Synology Drive can use snapshot technology and, compared with ext4, its database on Btrfs can save storage space up to 50% when storing historical file versions.
ext4
Important note
The knowledge base also states that it is not possible to change the file system of a volume once it has been created. The recommended method is to back up data from the ext4 volume and transfer it to a newly created Btrfs volume.
If you want, I can also summarize this as a simple “choose Btrfs if…, choose ext4 if…” decision list.
Sources used: [9], [12]