Available storage inside the container when device size is configured

LXD
1

Hello,

Is it possible to have a container seeing the available storage on a device equal to the size defined in the container definition instead of the full available storage of the pool the device belongs to?

In the following example I would like container guest to show Avail=10G instead of Avail=875G when issuing df -hT / in it.

user@host:~$ lxc storage list
+--------+--------+--------------+-------------+---------+
|  NAME  | DRIVER |    SOURCE    | DESCRIPTION | USED BY |
+--------+--------+--------------+-------------+---------+
| pool01 | btrfs  | /media/lxdsp |             | 7       |
+--------+--------+--------------+-------------+---------+
user@host:~$ df -hT /media/lxdsp/
Filesystem     Type   Size  Used Avail Use% Mounted on
/dev/sda2      btrfs  887G  9,9G  875G   2% /media/lxdsp
user@host:~$ lxc config device get guest root size
10GB
user@host:~$ lxc exec guest bash
root@guest:~# df -hT /
Filesystem     Type   Size  Used Avail Use% Mounted on
/dev/sda2      btrfs  887G  9.9G  875G   2% /

I know that the storage quota should be enforced in any case, but still I would like if this behaviour is at all possible, even if with other storage backends and/or configuration.

Thanks in advance!

2

Hi @pmarini,
You can check the expanded configuration of the container like that, lxc config show guest --expanded and add / override the root disk size as well.
lxc config device override quest root size=15GB
You can adjust the root disk size in your requirement, here is the document link.
https://linuxcontainers.org/lxd/docs/master/storage/
Regards.

3

Hi @cemfazer.

Thanks for the reply but this is not my question.

What I want to understand is if it is possible and makes sense to have the df -hT inside the container reflecting the size set in the host.

4

By default BTRFS volumes do not have a quota enforced, this is why you are seeing the full storage pool size available.

Have you tried setting a quota as @cemzafer suggested?

5

Yes I tried. Everything works fine, quota is enforced, meaning that trying to push a file larger than the quota makes the operation fails.

My concern is to expose this information also to the df utility inside the container, “Avail” field.

6

btrfs unfortunately does not expose quotas through the statvfs syscall and so df will never show a btrfs quota.

That’s different from what ext4/xfs/zfs/… all do where the filesystem stat information reflects the quota in place.

2 Likes
7

Ok, thanks for the clarification.

If there is some good read comparing storage backend types for LXD apart of the Storage configuration page, I would be glad to know.