I understand that docker containers have a maximum of 10GB of disk space with the Device Mapper storage driver by default.
In my case, I have a worker container and a data volume container. I then link them together using "-volumes-from". I also use the Device Mapper storage driver.
Example, I did a test by creating a script to download a 20GB file onto my data volume container and that worked successfully.
My question, is there a 10GB quota for the data volume container? How did the 20GB file download successfully if it is limited by 10GB?
Volumes are outside of the Union File System by definition, so any data in them will not count towards the devicemapper 10GB limit. By default volumes are stored under /var/lib/docker/vfs if you don't specify a mount point.
You can find the exactly where your volumes are on the host by using the docker inspect command e.g:
docker inspect -f {{.Volumes}} CONTAINER
You will get a result like:
map[/CONTAINER/VOLUME:/var/lib/docker/vfs/dir/5a6f7b306b96af38723fc4d31def1cc515a0d75c785f3462482f60b730533b1a]
Where the path after the colon is the location of the volume on the host.
Related
This might come across as a stupid question, but I am unable to figure something about docker volumes. Going through the official documentation I can see that we can map the host machine file system on the container for persistent storage. Following the instruction I was successfully able to mount a folder on my container.
Once I exec bash into the container, I can see the mapped directory structure there as expected. My question is, how is the data mapped between these two paths, that is from the container to the mount volume on host OS. Is the data duplicated or the container directly stores the data on the volume on host OS and the mapped paths are shown for something like symlink ?
This question comes across since we are trying to maintain a large amount of data on a mounted disk but accessible by the container, with the assumption that mounting volume would directly store the data on the disk and nothing on the container.
The Docker documentation refers to this type of mount as a "bind mount"; that's also a technical Linux term that allows one part of the filesystem to also appear somewhere else, and there's a mount --bind option you can use outside of Docker (usually a pretty specialized option).
On native Linux, the host content and the container-visible content are literally the exact same disk content. If you have a bind-mounted host directory or a named Docker volume mounted over a container directory, all reads and writes will use that mounted content, and in fact nothing will be written to the container filesystem on that path.
You mention symlinks; these are always resolved as filenames in their respective filesystem space. If the mounted filesystem has a symlink passwd -> /etc/passwd then reading it will yield the host's password file on the host, and the container's password file inside the container. If it has a symlink f -> ../f then it will look at the directory above the mount point in whichever the local filesystem is.
On non-Linux this process is a little bit more technically complex since there is typically a Linux virtual machine involved in the mix. This usually manifests as file synchronization appearing slow. For data you don't need to directly access as a human, storing it in a named Docker volume will usually be faster.
In docker, where is the container data, apart from the mounted volume, is stored till the container is running.
So lets say /usr/local is volume mounted, so it would be shared between the host and the container. Where is everything else stored?
You should inspect your docker container
docker inspect [ID_CONTAINER]
and check for the fields MergedDir, LowerDir and UpperDir. Docker uses OverlayFS file system to store the data.
OverlayFS layers two directories on a single Linux host and presents them as a single directory. These directories are called layers and the unification process is referred to a a union mount. OverlayFS refers to the lower directory as lowerdir and the upper directory a upperdir. The unified view is exposed through its own directory called merged.
Check the doc here.
You can run the following command to get container written data
ll `podman inspect ContainerName --format "{{ .GraphDriver.Data.MergedDir }}"`
First time docker ser here, running on Raspberry Pi 3 (Hypriot OS). I have an external hdd attached to my raspberry pi to store all the files. The os is on the sdcard.
I am setting up many images on docker: sonarr, radarr, emby server and bittorrent client.
I have created all containers following the lines on docker hub page, so I attached all of the folders using mount bind (-v /some/path:/some/path).
Now the documentation says volume is better because it doesn't rely on filesystem. Also, I am having problems because I want to use hardlink between files on my external hdd, but because I am using mount binds, it seems to not work when calling hardlink from one mount to another on the same hdd. I think adding only one mount bind should solve this but I just want to make the config correct now.
Is volume an option to store all the movies or should I keep using mount bind?
In canse of volume, can I specify the external hdd to store movies? I have docker installed on an sdcard but I need the movies on my external hdd.
I have used docker create volume --name something -o device=/myhddmount/ but I am not sure if this is ok, because docker volume inspect shows a mountpoint on the sdcard. Also, when I create the volume, should I set -o type=ext4? because according to the manual etx4 doesn't has a device= option.
Thanks!
I have a docker container which does alot of read/write to disk. I would like to test out what happens when my entire docker filesystem is in memory. I have seen some answers here that say it will not be a real performance improvement, but this is for testing.
The ideal solution I would like to test is sharing the common parts of each image and copy to your memory space when needed.
Each container files which are created during runtime should be in memory as well and separated. it shouldn't be more than 5GB fs in idle time and up to 7GB in processing time.
Simple solutions would duplicate all shared files (even those part of the OS you never use) for each container.
There's no difference between the storage of the image and the base filesystem of the container, the layered FS accesses the images layers directly as a RO layer, with the container using a RW layer above to catch any changes. Therefore your goal of having the container running in memory while the Docker installation remains on disk doesn't have an easy implementation.
If you know where your RW activity is occurring (it's fairly easy to check the docker diff of a running container), the best option to me would be a tmpfs mounted at that location in your container, which is natively supported by docker (from the docker run reference):
$ docker run -d --tmpfs /run:rw,noexec,nosuid,size=65536k my_image
Docker stores image, container, and volume data in its directory by default. Container HDs are made of the original image and the 'container layer'.
You might be able set this up using a RAM disk. You would hard allocate some RAM, mount it, and format it with your file system of choice. Then move your docker installation to the mounted RAM disk and symlink it back to the original location.
Setting up a Ram Disk
Best way to move the Docker directory
Obviously this is only useful for testing as Docker and it's images, volumes, containers, etc would be lost on reboot.
Normally we would run container by using the following command:
Docker run -it ubuntu /bin/bash
Is there any option to specify where to run the container (like on which disk or partition)?
Do you mean where the container data/layers will be stored?
The layers are all inside /var/lib/docker/(aufs)
It's possible for you to mount a different larger/faster partition into this folder, but this is for the entire docker platform. if you are careful, you can mount the partition for a particular docker container.
It would be better if you would use "docker run -v folder:mount point" flag, since you can mount specific host folders as external volumes inside the container.
Both these can help you spread data over different partitions/disks.
I am not aware of a container specific option.
However, you can bind-mount (or create a symlink) a particular disk or partition to '/var/lib/docker'. This will make all the container storage to be on that partition.
If you want the container storage to be on multiple partitions, LVM is an option.
You can setup a volume group that spans multiple partitions. You can then ask the Docker daemon to create a thinly provisioned logical volume in one of these volume groups to be used as storage.
The following link provides more information : https://access.redhat.com/documentation/en/red-hat-enterprise-linux-atomic-host/7/getting-started-with-containers/chapter-7-managing-storage-with-docker-formatted-containers
Also, using a union mount like OverlayFS could be another solution : https://askubuntu.com/questions/109413/how-do-i-use-overlayfs