Not a fan of device mapper in Linux

Yeah, I know. It brings all manner of capabilities with it. Its just the cost of these capabilities, when combined with other tools, like, say, Docker, that make me not want to use it.

To wit:

root@ucp-01:~# ls -alF /var/lib/docker/devicemapper/devicemapper/
total 52508
drwx------ 2 root root           80 Jan 29 22:38 ./
drwx------ 4 root root           80 Jan 29 22:38 ../
-rw------- 1 root root 107374182400 Jan 29 22:39 data
-rw------- 1 root root   2147483648 Jan 29 22:39 metadata

root@ucp-01:~# ls -halF /var/lib/docker/devicemapper/devicemapper/
total 52M
drwx------ 2 root root   80 Jan 29 22:38 ./
drwx------ 4 root root   80 Jan 29 22:38 ../
-rw------- 1 root root 100G Jan 29 22:39 data
-rw------- 1 root root 2.0G Jan 29 22:39 metadata


root@ucp-01:~# ls -salF /var/lib/docker/devicemapper/devicemapper/
total 52508
    0 drwx------ 2 root root           80 Jan 29 22:38 ./
    0 drwx------ 4 root root           80 Jan 29 22:38 ../
51820 -rw------- 1 root root 107374182400 Jan 29 22:39 data
  688 -rw------- 1 root root   2147483648 Jan 29 22:39 metadata

Sure, it takes up 52MB of space. But its done a nice sparse allocation of 100GB and 2GB for metadata.

I am working on switching this off of device mapper (it has only given me grief in other contexts), and onto overlayfs as a better choice. Its needed as this is one of our ramboot file systems, and I really don’t want to see that sparse file get filled.

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