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Loopback storage devices

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?

1 Like

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

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

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.

Thanks for the reply!

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