This is a request for a new feature in unison:

I am syncing two locations via a usb flash drive (i.e. moving it
between the machines and syncing each with the drive).

The flash disc is 128 mb, but I want to sync directories of about 1gb

This is not possible at the moment as unison stores a copy of all
files on the usb drive.
It should not need to do this - it could tell if a file has changed
just by storing the filename & date (and perhaps checksum).

So it would be nice for unison to optionally use a different algorithm
when using a removable drive.
This algorithm would look like this:

Each file can be represented by a 'token' that consists of the
filename, checksum & date.
On the removable disk, it stores the directory structure as before,
but all files are normally replaced by their tokens.

When unison syncs, if it detects the file token is older than the file
being synced with, it copies the actual file onto the disk in place of
the token.
If it detects an actual file on the removable disk and this is newer
than the other file, then it replaces the other file with the file on
the removable disk & then replaces the file on the removable disc
with a token.

You could extend this to syncing > 2 sets of directories by storing 1
token for each set being synced.


how difficult would this enhancement be and what are the chances of it
happening?

regards,

Tom