Bit new to Docker - so does this mean Docker 1.7 won't work with RHEL? Specifically I'm working on RHEL 6.6 machines, and I'm already stuck with Docker 1.5 so curious to know whether this will affect me
I'm not running RHEL myself, so I can't authoritatively speak about it. The backstory is that Docker, as statically compiled and released, uses the 1.02 release of the devicemapper driver, which has a bug in it. The OS has a 1.02.1 version (and has, for some time, it was patched in Dec 2013), but you have to make your own Docker build which will dynamically link to it.
Take a look at your version of libdevmapper, and you should be able to see if there will be a problem; what I've heard is that CentOS and RHEL also have a fixed version of devicemapper, which causes the mis-match and creates the problem outlined in the #4036 issue.
The ideal fix is to actually compile Docker on an Ubuntu (RHEL) OS when building the Ubuntu (RHEL) packages, but what's actually happening is that it's being built in a minimal Linux container - which gives it a different version.
Take a look at your version of libdevmapper, and you should be able to see if there will be a problem; what I've heard is that CentOS and RHEL also have a fixed version of devicemapper, which causes the mis-match and creates the problem outlined in the #4036 issue.
The ideal fix is to actually compile Docker on an Ubuntu (RHEL) OS when building the Ubuntu (RHEL) packages, but what's actually happening is that it's being built in a minimal Linux container - which gives it a different version.