Docker Discuss Using Docker on CentOS 7 ? Choose EXT4 over XFS

Another gotcha moment I came across playing with Docker on CentOS 7 in that new Docker versions will need d_type support enabled in filesystem. Docker requires CentOS 7 to use and CentOS /RHEL 7 by default create XFS filesystems with d_type=0 disabled instead of d_type=1. CentOS 7 though creates EXT4 filesystems with d_type=1 enabled by default. See explanation at What is d_type and why Docker overlayfs need it - Linuxer Pro.

Worse thing is you can't fix it on existing CentOS 7 created XFS partitions. You need to recreate the filesystem if you setup CentOS 7 filesystem with XFS partitions !

Docker info command error when d_type=0 and status on CentOS 7.3 virtualbox install

Code (Text):

docker info
Containers: 0
 Running: 0
 Paused: 0
 Stopped: 0
Images: 0
Server Version: 17.06.0-ce
Storage Driver: overlay
 Backing Filesystem: xfs
 Supports d_type: false

Code (Text):

WARNING: overlay: the backing xfs filesystem is formatted without d_type support, which leads to incorrect behavior.
        Reformat the filesystem with ftype=1 to enable d_type support.
        Running without d_type support will not be supported in future releases.

Docker info command when d_type=1 enabled on CentOS 7.3 system with EXT4 filesystem

Code (Text):

docker info
Containers: 1
 Running: 0
 Paused: 0
 Stopped: 1
Images: 4
Server Version: 17.06.0-ce
Storage Driver: overlay
 Backing Filesystem: extfs
 Supports d_type: true

---

 

Guess one solution is if you have free unallocated disk space, you can create a filesystem with d_type=1 enabled and change Docker's default data directory path from /var/lib/docker to point to the new filesystem

• How to change docker installation directory in centos 7 with docker 1.13 version
• Control and configure Docker with systemd

i.e. setting up custom settings in /etc/docker/daemon.json

default Docker root directory where data is located

Code (Text):

docker info 2>&1 | grep Root
Docker Root Dir: /var/lib/docker

from Fix strange chown error during Discourse bootstrap or rebuild - Linuxer Pro

 

Mentioned in RHEL 7.2 preview docs for overlayfs filesystem though Chapter 21. File Systems

 

nah I haven't only really read the tracker, never submitted to it before heh.

edit: seems similar bug at 0012031: Removing files located in a lowerdir in an overlay fs is erroneous - CentOS Bug Tracker

 

Yeah but could be argued it's in Docker documentation Use the OverlayFS storage driver so if you use Docker ensure XFS filesystem uses ftype=1 or use EXT4 I guess.

Guess it's partly on me not reading the latest version of the documentation heh.

Good news is from checking, DigitalOcean, Vultr, and Linode all default to using EXT4 filesystem for CentOS 7 instead of CentOS 7 default XFS. Guess it's for resizing downward support. So CentOS 7 on these VPS providers will be fine with Docker and overlayfs usage as ftype=1 is set.

Which means only folks inconvenienced would mainly be non-vps/cloud dedicated server uses who most likely will partition their own drives etc. So should properly partition or leave unallocated space at initial install time to be facilitate creating a XFS ftype=1 enabled filesystem(s) for their Docker usage.

 

example of this issue playing out when folks try to use Discourse on CentOS 7 via docker when XFS filesystem created with ftype=0 / d_type disabled

• Installation failing on CentOS 7.3
• Bootstrap fails on CentOS 7