Annexed data is stored inside your git repository's
Some special remotes can store annexed data elsewhere.
It's important that data not get lost by an ill-considered
git annex drop
command. So, git-annex can be configured to try
to keep N copies of a file's content available across all repositories.
(Although untrusted repositories don't count toward this total.)
By default, N is 1; it is configured by running
git annex numcopies N.
This default can be overridden on a per-file-type basis by the annex.numcopies
.gitattributes files. The --numcopies switch allows
temporarily using a different value.
git annex drop attempts to check with other git remotes, to check that N
copies of the file exist. If enough repositories cannot be verified to have
it, it will retain the file content to avoid data loss. Note that
trusted repositories are not explicitly checked.
For example, consider three repositories: Server, Laptop, and USB. Both Server
and USB have a copy of a file, and N=1. If on Laptop, you
git annex get
$file, this will transfer it from either Server or USB (depending on which
is available), and there are now 3 copies of the file.
Suppose you want to free up space on Laptop again, and you
git annex drop the file
there. If USB is connected, or Server can be contacted, git-annex can check
that it still has a copy of the file, and the content is removed from
Laptop. But if USB is currently disconnected, and Server also cannot be
contacted, it can't verify that it is safe to drop the file, and will
refuse to do so.
With N=2, in order to drop the file content from Laptop, it would need access to both USB and Server.
For more complicated requirements about which repositories contain which content, see required content.