Add overlay as default storage driver instead of devicemapper

[praveenkumar]

Since overlay is already part of linux kernel since 3.18 and for our ISO's it make complete sense to use overlay driver instead devicemapper for docker.

$ minishift ssh
$ lsmod | grep overlay
overlay                               47399    0

[LalatenduMohanty]

@praveenkumar I think we should wait for RHEL and CentOS to move to overlay. I agree that overlay is better but do not want to get in to issues which RHEL or CentOS has not encountered yet.

[LalatenduMohanty]

Found https://access.redhat.com/solutions/1616743 and seems like it is still in tech preview.

[praveenkumar]

Found https://access.redhat.com/solutions/1616743 and seems like it is still in tech preview.

According to that devicemapper is not supported. Even http://www.projectatomic.io/blog/2015/06/notes-on-fedora-centos-and-docker-storage-drivers/ discourage to use devicemapper and have overlay as alternative.

I think we should wait for RHEL and CentOS to move to overlay.

RHEL-7.3 and latest CentOS already have overlay module in the kernel, I am not sure what else we have to wait for?

[LalatenduMohanty]

@praveenkumar I think we agree that we should use device mapper thin provisioning as used by CentOS and RHEL Atomic host and recommended by OpenShift [2]. But it is not possible with current live ISO . So looks like we do not have any choice left as device mapper with loopback device should be avoided [3] . I was under an impression that we are using device mapper thin provisioning similar to CDK and ADB.

So +1 for move to overlayfs, but it has some prerequisites like SELinux and XFS [1]. If we can meet the prerequisites we should be ok I think.

[1] https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/7/html/7.2_Release_Notes/technology-preview-file_systems.html [2] https://docs.openshift.com/container-platform/3.3/install_config/install/host_preparation.html#configuring-docker-storage [3] http://www.projectatomic.io/blog/2015/06/notes-on-fedora-centos-and-docker-storage-drivers/

[praveenkumar]

So +1 for move to overlayfs, but it has some prerequisites like SELinux and XFS [1]. If we can meet the prerequisites we should be ok I think.

Currently we have SELinux already disabled and we are using ext4 filesystem for our centos/rhel template so both prerequisites already in place. What I want to try how OCP behave in disabled mode of SELinux.

[hferentschik]

So where are we with this? Is the conclusion so far to use overlay?

[coolbrg]

@LalatenduMohanty @hferentschik Moved to 1.5.0 at the moment.