I am just a little confused about an expression in Reference Book:
This directory contains many variable files, including logs, temporary caches, third party products in /var/opt, and is the default location for virtual machine images and databases. Therefore this subvolume is created to exclude all of this variable data from snapshots and has Copy-On-Write disabled.
And according to this section, YaST seems to disable Copy-On-Write of /var by adding a nodatacow mount option by default.
However, according to btrfs(5), it seems impossible to set per-subvolume nodatacow, nodatasum, or compress using mount options. These mount options will apply to the whole filesystem.
So how does openSUSE disable Copy-On-Write of /var subvolume? I think with nodatacow mount option, the whole filesystem will have Copy-On-Write disabled, and we will lose it benefit.
In particular, I have Snapshot disabled when installing the system, and enable it after installing. Then I notice the expression in Reference Book, so I check my /etc/fstab, there is no nodatacow mount option of /var subvolume, so I wonder if I should add this mount option.
I would be glad if someone could help me clarify this, thanks!