Lxd vm slow write performance BTRFS

when i am running this command

lxc storage create new_pool zfs zfs.pool_name=zfspool

it tels me that the pool allredeay exist?

Please post the lxc storage ls.
Regards.

i allredeay got it.

Is it correct that when i use zfs with lxd i can not mount dataset because its legacy?

Should i change this? or keep it this way?

As stated in here, but you dont need to mount zfs pool/filesystem by manually at boot zfs mounted by zfs-mount.service. Keep that way.
Regards.

If the value is legacy, then ZFS will not mount the filesystem, 
but you can use mount and umount to manage the filesystem's 
mountpoint manually. You could also use /etc/fstab to guide 
automatic mounting.

LXD uses legacy mount option to prevent ZFS from mounting the volume until its needed.
It also avoids some issues with ZFS inside the LXD snap mount namespace by avoiding the parent data sets from being mounted on the host.

Generally speaking avoid mounting LXD managed volumes manually.