"As part of our backup process, Backblaze will run a checksum against each file before uploading it. This requires the entire bzfileids.dat file to be loaded into RAM. After a long time, or if you have an extraordinarily large number of files, the bzfileids.dat file can grow large causing the Backblaze directory to appear bloated, and use more RAM (potentially slowing down your system). In your case your bzfileids are extremely large, likely because you have a lot of files and an older backup."
here's my backblaze folder: http://imgur.com/ohqUERr (i have my temporary data drive set to a secondary drive)
What kind of internet connection are you on? I recently reinstalled my mac from scratch (El Capitan upgrade went haywire) and had to redo my backblaze backup. I uploaded the 500 GB to Backblaze in under 24 hours.
Also, could it be that the "re-upload" was able to detect your older copy of the files and reuse them? I can rsync terabytes in minutes over slow connections when the other side already has the files ...