RAID on NextCloud

Manik Taneja manik at
Wed Mar 15 22:18:15 UTC 2017

much appreciated simon!

On Tue, Mar 14, 2017 at 11:13 PM, Simon Fels <simon.fels at>

> On 15.03.2017 00:39, Manik Taneja wrote:
> > hi there,
> >
> > an interesting question came up on askubuntu-
> >
> >
> >
> > is the best solution to package mdadm as a snap with core providing
> > an interface to /dev/md*? are there alternate solutions?
> We had a pretty active discussion a while back when we implemented the
> udisks2 interface in snapd. The outcome was that we don't want to give
> arbitrary snaps access to block devices and added all access for those
> directly into the udisks2 interface (see [0]).
> udisks2 offers a mediated way for all other snaps to deal with block
> devices and generally also allows working with RAIDs. I say generally,
> because this is a feature we didn't verified yet that it is working with
> the udisks2 snap currently in the store.
> If support for RAIDs in udisks2 works users should be able to mount a
> RAID on a directory in /media via an dbus API call.
> One downside is that the udisks2 interface explicitly denies plug
> connections as it still gives kind of privileged access to the system.
> Every mount done via udisks2 will appear below /media and every snap
> using the removable-media interface will get access to devices mounted
> there, regardless if it's the system partition or not. So even the plug
> side is a very privileged thing. That said, snaps can ask for a
> snap-declaration on the store side to get connections to udisks2.
> Another feature we support with the udisks2 snap is auto-mounting. This
> allows a device to say that it wants removable devices like USB storage
> device to be automatically mounted in /media as you know it from
> consumer oriented devices like the Ubuntu Desktop. Depending on how the
> RAID is setup this might be able to get the the RAID mounted on boot
> into /media. Requirements for the automounter to consider a device are
> currently:
>  * Device is not a system device (meaning its not a partition on the
> device we're booting the system from)
>  * Device is not already mounted
>  * Device is a removable devices (USB, CD/DVD)
> For a very simple, unconfined solution you could just install the
> udisks2 snap (given that it detects and works well with RAID devices)
> and create a systemd unit in /etc/systemd/system/mount-my-raid.service
> [Unit]
> Description=Mount my RAID
> [Service]
> Exec=/snap/bin/udisks2.udisksctl mount -b /path/to/block/device
> [Install]
> Then activate it via
> $ sudo systemctl enable mount-my-raid.service
> and the RAID should be automatically mounted below /media on the next
> system reboot.
> I hope this helps.
> Btw. I will post this as an answer to the question too.
> regards,
> Simon
> [0]:
> builtin/udisks2.go
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