The I/O in the Docker containers is not very stable. When we download a zip file from a container the download time is very jumpy. When we look at the IO usage on the Docker engine (running on CentOS 6.7) with ‘iotop’ we see that the reading is changing a lot between 500 Kb and 10Mb. The containers and the host are not very busy, CPU usage is around 10% and memory usage about 25% and those are stable when the download is busy.
When we download a file from the Docker host it is stable, it seemed like that the Docker engine is the cause of the unstableness. Does anyone has a clue for this?
Next to this the containers respond sometimes very fast as expected, but sometimes also have delays of about 10 to 30 seconds to show a simple webpage on Nginx or Apache. Probably also the same issue.
Running Docker engine 1.7.1 on CentOS 6.7 which is running in a VM.
mount ; docker info /dev/mapper/vg_centos6-lv_root on / type ext4 (rw) proc on /proc type proc (rw) sysfs on /sys type sysfs (rw) devpts on /dev/pts type devpts (rw,gid=5,mode=620) tmpfs on /dev/shm type tmpfs (rw) /dev/sda1 on /boot type ext4 (rw) none on /proc/sys/fs/binfmt_misc type binfmt_misc (rw) Containers: 10 Images: 265 Storage Driver: devicemapper Pool Name: docker-253:0-1835199-pool Pool Blocksize: 65.54 kB Backing Filesystem: extfs Data file: /dev/loop0 Metadata file: /dev/loop1 Data Space Used: 13.55 GB Data Space Total: 107.4 GB Data Space Available: 93.82 GB Metadata Space Used: 19.08 MB Metadata Space Total: 2.147 GB Metadata Space Available: 2.128 GB Udev Sync Supported: true Deferred Removal Enabled: false Data loop file: /var/lib/docker/devicemapper/devicemapper/data Metadata loop file: /var/lib/docker/devicemapper/devicemapper/metadata Library Version: 1.02.95-RHEL6 (2015-07-29) Execution Driver: native-0.2 Logging Driver: json-file Kernel Version: 2.6.32-573.3.1.el6.x86_64 Operating System: <unknown> CPUs: 4 Total Memory: 11.63 GiB