Before version 2 of the git-annex repository, files added to the SHA
[[backends]] did not have their file size tracked, while files added to the
WORM backend did. The file size information is used for disk free space
checking.

Files added to the SHA backends after the conversion will have their file
size tracked automatically. This disk free space checking is an optional
feature and since you're more likely to be using more recently added files,
you're unlikely to see any bad effect if you do nothing.

That said, if you have old files added to SHA backends that lack file size
tracking info, here's how you can add that info. After [[upgrading|upgrades]]
to repository version 2, in each repository run:

	git annex migrate
	git commit -m 'migrated keys for v2'

The usual caveats about [[tips/migrating_data_to_a_new_backend]]
apply; you will end up with unused keys that you can later clean up with
`git annex unused`.
