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I'm running apache in a docker container on a CentOS 7 machine with devicemapper (on a dedicated volume group not on loopback file).

After a few requests, system load dramatically increase even up to 20. Since the cpu load is reasonably low, i traced down the I/O activity with iotop -a and discovered that while the container is running the process [loop0] does a lot of reading from disk.

I googled a bit but i can't still figure out what is [loop0] for. Can someone give me a clue? Can a process running inside a docker container, cause [loop0] to go nuts?

user1328830
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1 Answers1

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You probably are using the default loopback storage backend. This backend uses a file on the host where it creates a logical volume from which it exposes a loop device to the docker containers.

This is why all IO is going through this process.

More info about loopback here

cristi
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