ZFS plugin: "mountpoint not unique"

birnbacs · 11. März 2018

I have a Debian machine that boots from a zpool on a pair of mirreored 1TB disks.
A third disk of 4TB disk with zpool 'ariadne' is available for sharing:

Code

zfs list
NAME                 USED  AVAIL  REFER  MOUNTPOINT
ariadne              312K  3,51T    96K  /mnt/ariadne
rpool               5,37G   894G    96K  /
rpool/ROOT           887M   894G    96K  none
rpool/ROOT/debian    887M   894G   816M  /
rpool/home           528K   894G    96K  /home
rpool/home/develop   108K   894G   108K  /home/develop
rpool/home/root      204K   894G   204K  /root
rpool/home/seb       120K   894G   120K  /home/seb
rpool/srv            100K   894G   100K  /srv
rpool/swap          4,25G   898G    64K  -
rpool/var            259M   894G    96K  /var
rpool/var/cache      256M   894G   256M  /var/cache
rpool/var/log       1,24M   894G  1,24M  /var/log
rpool/var/spool      712K   894G   712K  /var/spool
rpool/var/tmp        128K   894G   128K  /var/tmp

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Now, when I select the ZFS plugin it gives me this error:

Code

The configuration object 'conf.system.filesystem.mountpoint' is not unique. An object with the property 'dir' and value '/' already exists.


Error #0: OMV\AssertException: The configuration object 'conf.system.filesystem.mountpoint' is not unique. An object with the property 'dir' and value '/' already exists. in /usr/share/php/openmediavault/config/database.inc:495 


Stack trace: 
#0 /usr/share/openmediavault/engined/rpc/fstab.inc(119): OMV\Config\Database->assertIsUnique(Object(OMV\Config\ConfigObject), 'dir') #1 [internal function]: OMVRpcServiceFsTab->set(Array, Array) 
#2 /usr/share/php/openmediavault/rpc/serviceabstract.inc(123): call_user_func_array(Array, Array) 
#3 /usr/share/php/openmediavault/rpc/rpc.inc(86): OMV\Rpc\ServiceAbstract->callMethod('set', Array, Array) 
#4 /usr/share/omvzfs/Utils.php(209): OMV\Rpc\Rpc::call('FsTab', 'set', Array, Array) 
#5 /usr/share/openmediavault/engined/rpc/zfs.inc(187): OMVModuleZFSUtil::fixOMVMntEnt(Array) 
#6 [internal function]: OMVRpcServiceZFS->getObjectTree(Array, Array) 
#7 /usr/share/php/openmediavault/rpc/serviceabstract.inc(123): call_user_func_array(Array, Array) 
#8 /usr/share/php/openmediavault/rpc/rpc.inc(86): OMV\Rpc\ServiceAbstract->callMethod('getObjectTree', Array, Array) 
#9 /usr/sbin/omv-engined(536): OMV\Rpc\Rpc::call('ZFS', 'getObjectTree', Array, Array, 1) 
#10 {main}

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my /etc/fstab reads:

Code

# UNCONFIGURED FSTAB FOR BASE SYSTEM
/dev/zvol/rpool/swap none swap defaults 0 0
# >>> [openmediavault]
# <<< [openmediavault]

It seems that every time I use OMV a new <mntent> is appended to the config.xml - which fails because the <dir> value is not unique.
Whenever I delete such an entry, a new one pops in:

Code

<mntent>
        <uuid>b63450e7-4c63-43e4-aefc-262d57d28e90</uuid>
        <fsname>rpool</fsname>
        <dir>/</dir>
        <type>zfs</type>
        <opts>rw,relatime,xattr,noacl</opts>
        <freq>0</freq>
        <passno>0</passno>
        <hidden>1</hidden>
      </mntent>

One strange thing is that the UUIDs change each time but are not familiar, that is to say they cannot be found under /dev/disk/...

Why does OMV keep inserting entries?
How can I set the list of zfs pools straight?
Does this behaviour have to do with the existing ZFS pools at all?
Is booting from ZFS a problem here?

Kind regards

birnbacs

subzero79 · 11. März 2018

I think booting from zfs is the issue. This was never accounted for, but I need to confirm this with testing.

For every dataset and pool the plugin inserts an entry in the db.

Now looking at the error and the zpool list I see there are two datasets pointing to the same mount point, maybe that’s the issue, the filesystem backend of Omv doesn’t allow this, because parsing the db all objects must be unique.

subzero79 · 11. März 2018

for sure this needs to be fixed either by the plugin or Omv, like goes against the usage guidelines in terms that by booting zfs is allowing to share system folders, which cannot be done in standard installs.

Cc:
@nicjo814

birnbacs · 11. März 2018

Agreed. IMO he plugin's task is only to manage the zfs entities so enforcing the guidelines is not up to it (and probably would not work anyway). On the other hand OMV does not support ZFS deeply enough to enforce the guidelines over ZFS peculiarlities.
It seems to me that OMV should be able to work with ZFS datasets even if the policy cannot be inforced properly. After all, a ZFS-booted machine is not a standard install and does not need 100% accounting for.

subzero79 · 11. März 2018

Yes but as for preventing using system folders there is already some steps in the plugin, but coming with a zfs rootfs is different.

The error at the moment is probably what I described above. Can you set the duplicate mount point to a single one (/)?

birnbacs · 12. März 2018

I would have loved to go for this option but the two conflicting ZFS elements are required for booting and I don't see how I could do without any one of them.

For installation I followed the (very good) instructions on
https://github.com/zfsonlinux/…ebian-Stretch-Root-on-ZFS
so maybe I will not be the only one with a layout like this.

Apart from ZFS administration OMV is completely usable without the plugin and there is no protection against sharing system folders. Being serious about the guideline will require handling it in core functionality.

I guess the usage rule "don't share the system disk" will have to be rephrased as a disk does not mean much on ZFS.

subzero79 · 12. März 2018

I followed this guide a few years ago for testing. Reading there i do not see why rpool needs to be pointed to /, rpoot/ROOT/debian points correctly, but the other one could be anywhere without pointing to / IMO, correct me if i am wrong and i missed something.

Zitat von birnbacs

Apart from ZFS administration OMV is completely usable without the plugin and there is no protection against sharing system folders. Being serious about the guideline will require handling it in core functionality.

I believe the changes need to be done at plugin level, but that's for more advanced developers. I have only submitted small patches to the plugin, this requires more work IMO.

Without the plugin the web panel is useless as you won't be able to create shared folders. If you have a small disk around to spare you can start mounting datasets to that disks in ext4 format to have them available without the plugin.

Zitat von birnbacs

I guess the usage rule "don't share the system disk" will have to be rephrased as a disk does not mean much on ZFS.

Well, the small patch i submitted was to cover this, as prevents to use any existing folder, given the fact that when datasets are created they generate the mount folder. In this case is different as they are already defined.

https://github.com/OpenMediaVa…penmediavault-zfs/pull/35

edit: i see point 2.3 that creates rpool at /, still curious if the system will boot without that mountpoint option.

birnbacs · 13. März 2018

Zitat von subzero79

Without the plugin the web panel is useless as you won't be able to create shared folders.

I may be getting you wrong here but with the plugin installed but effectively nonfunctional all sharing functions are available. Creating shared folders, assigning privileges and all. What is missing is creating and maintaining datasets, making snapshots etc.

Zitat von subzero79

edit: i see point 2.3 that creates rpool at /, still curious if the system will boot without that mountpoint option.

Me too but I would hate to render my system unbootable. Not sure how to change that back from a live USB install.

Let's see if I can work up the courage today to try changing the / mountpoint as explained here:
https://unix.stackexchange.com…ount-point-for-a-zfs-pool

That way I could see what is inside and whether or not it is necessary for booting.

birnbacs · 13. März 2018

Zitat von subzero79

Without the plugin the web panel is useless as you won't be able to create shared folders.

I may be getting you wrong here but with the plugin installed but effectively nonfunctional all sharing functions are available. Creating shared folders, assigning privileges and all. What is missing is creating and maintaining datasets, making snapshots etc.

Zitat von subzero79

edit: i see point 2.3 that creates rpool at /, still curious if the system will boot without that mountpoint option.

Me too but I would hate to render my system unbootable. Not sure how to change that back from a live USB install.

Let's see if I can work up the courage today to try changing the / mountpoint as explained here:
https://unix.stackexchange.com…ount-point-for-a-zfs-pool

That way I could see what is inside and whether or not it is necessary for booting.

subzero79 · 13. März 2018

The plugin implements a filesystem backend, means every dataset and pools are registered in the internal database of omv. This creates volumes that you see in shared folders dropdown menu. If you deleted the plugin the dataset entries on the omv database might still be there (not sure if postrm deletes this points at plugin removal), but for sure if you go the fs section with zfs entries in the db you should see an error like "no filesystem support for zfs" if there is no plugin installed

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