Arch Linux

kevdog

Member

Registered: 2013-01-26

Posts: 107

ZFS - How to add and mount datasets to a running pool?

Thanks to the great arch forums and useful blog by John Ramsden (https://ramsdenj.com/2016/06/23/arch-li … tall-setup), I've managed to set up a ZFS on root installation within xcp-ng (opensource Xen hypervisor).

I originally created datasets during installation and in the arch-chroot environment, however after using the system for a while I wanted to add and mount and additional data set.

 kevdog@arch-TM zfs list                             ✔  127  12:11:55
NAME                          USED  AVAIL     REFER  MOUNTPOINT
zroot                        4.60G   188G       24K  /zroot
zroot/data                   3.03G   188G       24K  none
zroot/data/timemachine       3.03G   188G     3.03G  legacy
zroot/sys                    1.57G   188G       24K  /zroot/sys
zroot/sys/arch               1.57G   188G       24K  none
zroot/sys/arch/ROOT          1.51G   188G       24K  none
zroot/sys/arch/ROOT/default  1.51G   188G     1.51G  /
zroot/sys/arch/home          54.1M   188G     54.1M  legacy
zroot/sys/arch/var           2.89M   188G       24K  /var
zroot/sys/arch/var/log       2.87M   188G     2.87M  legacy

I added the data and /data/timemachine to zroot after installation.
Because /zroot/data/timemachine is using legacy mounting I adjusted the fstab accordingly:

 kevdog@arch-TM  ~  cat /etc/fstab                       ✔  128  12:13:44
# Static information about the filesystems.
# See fstab(5) for details.

# <file system> <dir> <type> <options> <dump> <pass>
# zroot/sys/arch/ROOT/default
zroot/sys/arch/ROOT/default	/         	zfs       	rw,xattr,noacl0 0

# /zroot
#/zroot              	/zroot    	zfs       	rw,xattr,noacl	0 0

# zroot/sys
#zroot/sys           	/zroot/sys	zfs       	rw,xattr,noacl	0 0

# zroot/sys/arch/home
zroot/sys/arch/home 	/home     	zfs       	rw,xattr,noacl	0 0

# zroot/sys/arch/var/log
zroot/sys/arch/var/log	/var/log  	zfs       	rw,xattr,noacl	0 0

# zroot/data/timemachine
zroot/data/timemachine	/mnt/timemachine   zfs          rw,xattr,noacl  0 0

My question is relation to the zpool export and import.  Since this is a zfs on root installation I had some concerns about umounting, exporting and importing.  Unabrazen, I proceeded and

 sudo umount -a 

But then was notified I couldn't unmount /var/log since volume was busy.  Since all volumes couldn't be unmounted, I couldn't export the pool

- Do I need to perform the the zpool export/import commands now that I have modified the dataset structure post arch installation? 
- If so, do I need to use the remastered archiso with zfs packages added that I used with the original installation?
Without performing any export/import, I've been able to reboot the system and have zoot/data/timemachine mount to /mnt/timemachine.

And lastly in general:
- Is there any advantages/disadvantages to declaring datasets with the legacy mountpoint property or should this be avoided?
I understand legacy mounts are handled through /etc/fstab and zfs mounts non-legacy mounts directly.
- Is there advantages/disadvantages to using one method over the other?