I have a current install of Sharepoint foundation 2010. It is using SQL Express and leveraging a BLOB store for the content database (only one content database) to get around the 10GB limitation of SQL express. There's about 80 gigs in the current BLOB store.
I setup sharepoint 2013, also with SQL express and setup the content database there with BLOB store as well (again only one content database). I then commenced to use the Sharegate tool (awesome stuff) to copy the old site, to the new. The copy failed with a "database full" error. And I was like.. wtf mate. The database on the current install of sharepoint 2010 is only 1.3GB. How did this one fill up?
So I go and look.. the target BLOB store (the physical folder for the BLOB store) has 20ish gigs of data.. so I know some data is getting to the BLOB store, but obviously some is...