[lxc-users] Limiting disk IO on LXD containers

[Ivan Ogai]

Greetings LXCers/LXDers

Just in case: I have also posted this question in discuss and
serverfault. By getting an answer here or there, I will answer the
others of course for everyone to find them. References at the end.


I have tried without success to limit the disk IO of a LXD container named *ci* with:

    lxc config device set ci root limits.read  30MB
    lxc config device set ci root limits.write 10MB

However, when running e.g. this command on the container:

    dd if=/dev/zero of=/root/testfile bs=1G count=10 oflag=direct

the result is the whole capicity of the disk, which is about **130MB/s**, instead of the expected result of about **10MB/s** for writing operations:

    10737418240 bytes (11 GB, 10 GiB) copied, 81,3877 s, 132 MB/s

This is also confirmed by `atop` running on the host.

**How can I effectively limit the disk IO of the container, so that no matter what happens on it, the host disk performance is not overcommitted**?

On a second test, I run the same *dd* command as above at the same time on the
guest and on the host, but the host is not prioritized either.


Some additional information:

- Host and guest are Ubuntu 16.04
- The server has two hard disks with equal partitions, joined in RAID 1 arrays
- On top of the biggest RAID array the root filesystem is mounted on a LVM volume group

        root at server ~ # lvs
        LV   VG   Attr       LSize
        root vg0  -wi-ao---- 2,72t
        swap vg0  -wi-ao---- 4,00g

- The LXD storage backend is *dir*

I could partitition the disk differently if that could help limiting disk IO of the container, e.g. having a RAID array dedicated to ZFS for LXD. **Would that help**?


Question references:
https://discuss.linuxcontainers.org/t/limiting-disk-io-on-lxd-containers/261
https://serverfault.com/questions/858873/limiting-disk-io-on-lxd-containers

-- 
Ivan