I am not sure this is the case, but from first-hand experience, it
sure looks like you can't turn on v7 (or really v6, actually) on a
single git worktree. For example, if I have my `pictures` repository
on `curie` and turn on v7, `angela` will *also* need to run `git annex
upgrade` on their worktree otherwise git-annex
(e.g. 6.20180913-1~bpo9+1 on Debian stretch) will be really confused:

    anarcat@angela:calendes$ less calendrier/calendes.pdf
    /annex/objects/SHA256E-s117451415--8d7d8366094a63c54bef99b5cd2e2b5187092f834d8bf7002e1d5fdceb38a710.pdf
    anarcat@angela:calendes$ git annex get calendrier/calendes.pdf
    anarcat@angela:calendes$ git annex whereis calendrier/calendes.pdf
    anarcat@angela:calendes$ # OMG WHERE ARE MY FILES! /me flails wildly

:)

It seems to me there should be a warning in the [[upgrades]] page
about this. I would have done so myself, but I'm not sure (like in my
last bug report) if I am doing things right.

In this case, this repository was already present (v5, indirect mode)
on both machines. I upgraded (using `git annex upgrade`) the
repository on curie (7.20181121 Debian buster) which went well.

(Then I messed around with that thumb drive, which led to
[[bugs/v7_fails_to_fetch_files_on_FAT_filesystem]], but probably
unrelated here.)

Then i powered on my laptop (`angela`) and saw the above. I would have
expected it to either upgrade automatically or warn me about the
repository inconsistency. Of failing that, the upgrades page should at
least warn us this is a "system-wide" (how do we call that?) change...

The workaround is to run `git annex upgrade` on that other repo, of
course, but if the source repo was also upgraded, it might be
difficult to sync files, as you will see that warning:

    $ git annex get
    get calendrier/calendes.pdf (from sneakernet...) 
    Repository version 7 is not supported. Upgrade git-annex.

Considering there's no backport of 7.x in Debian stretch, it makes the
upgrade path rather delicate... Is there a way to "downgrade" that
sneakernet repo? :) (Thankfully, the main server still runs v5 so the
files are still accessible from stretch....) -- [[anarcat]]

Updated the [[upgrades]] page, [[done]].
