The previous wording for the max_local_block_devices config option made
it sound like if you set it to 0 that you could restrict to only booting
instances from volumes, which is not the case - but is apparently
something that some operators want (this came up in the related bug and
This updates the help text with a description that ndipanov put in the
bug report which makes the 0 case more clear.
Co-Authored-By: Nikola Dipanov <email@example.com>