Docker IOPS and Read/Write limitations not being applied

Question

I used following command to test if the IOPS and Disk read/write limitations are being applied or not, but they are not. as soon as i run command, the disk uses 100% of IO and bandwidth. thought, i tried chancing the disk, i am not sure which disk i should use as i have xvda, xvdf, and dm0-dm8.

docker run --rm --device-read-bps=/dev/dm-0:1000 --device-write-bps=/dev/dm-0:1000 --device-read-iops=/dev/xvdf:20 --device-write-iops=/dev/xvdf:20 nginx bash -c "time dd if=/dev/zero of=testdocker bs=512k count=1000 oflag=dsync"

What could be reason that its not working? OS is ubuntu and docker version is: Docker version 1.13.0, build 49bf474

With slightly modified command, i gave it direct path where to write test file, but now it gets stuck and does nothing, just hangs there

docker run --rm -v "/dc:/dc" --device-read-bps=/dev/xvda:1m --device-write-bps=/dev/xvda:1m --device-read-iops=/dev/xvda:100 --device-write-iops=/dev/xvda:100 nginx bash -c "time dd if=/dev/zero of=/dc/testdocker bs=512 count=1000 oflag=dsync"

After this command, the IOWAIT become 100% and docker contains just Hangs, does nothing. i cannot even stop it or even do anything to it.

Answer 1

Control Groups v1 cannot limit buffered IO which is the vast majority of IO on a system.

Control Groups V2 can. If you are using a v2 compatible kernel (and if docker supports it, as I dont know if it does) you should use that instead.