zfs xattr=sa

yes, at least for non-zvol datasets (i.e., the files on the host and container volumes). but be aware that this is a ZFS-on-Linux only feature, so no sending datasets to OpenZFS/Solaris/FreeBSD/..
 
zvols don't have an xattr property as there are no xattrs that could be stored ;)
 
sure, if you don't need to import the pool on non Linux systems
 
How can I set xattr=sa at PVE-installation? As I see, xattr has "sa" value only for /data/subvols, but for /ROOT, /ROOT/pve-s and /data it has value "on"...
 
you cannot set it at installation time, but afterwards using 'zfs set'. most properties get inherited, so you can set it on rpool/data or rpool and it will apply to that and everything below.
 
But if I set those properties after installation, those changed xattr-types are used only for new writes, aren't they? That's too late...
 
But if I set those properties after installation, those changed xattr-types are used only for new writes, aren't they? That's too late...

yes, changed properties are only used for newly written files. but in case of xattr, after a default PVE install the root partition/dataset (which is the only one with actual stuff written) does not have a single file with an xattr set.. so just set it before you setup a samba/NFS server or create any containers (or whatever else you use xattrs for ;))