Loopback storage devices

General
1

I see the below message when I run docker info.

Data loop file: /var/lib/docker/devicemapper/devicemapper/data
WARNING: Usage of loopback devices is strongly discouraged for production use. Use --storage-opt dm.thinpooldev to specify a custom block storage device.
Metadata loop file: /var/lib/docker/devicemapper/devicemapper/metadata

I’ve been looking around trying to find what exactly the issues caused by using loopback devices in production are and I can’t find a thing. Just lots of people saying don’t do it.

Can anybody enlighten me to what the actual consequences of this are?

2

Hi Rubrown
Did you get the answer? I am also looking for the answer of this question.
Thanks.

3

For us it made problems when using docker compose.yml from UCP - used to get stuck
and couldt attache network bridge to a containers.

4

loop device is not recommended for production and performance problems https://docs.docker.com/engine/userguide/storagedriver/selectadriver/#/future-proofing . Check the info https://github.com/docker/docker/blob/master/daemon/graphdriver/devmapper/README.md#theory-of-operation , loopback devices are too slow for a production workload. If you have doubts why don’t you try to measure some test with and without loop device.

5

Thanks for the reply!

We moved on to thinpools shortly after posting this query. It’s good to know some of the specific benefits.