[Sirtel]

I keep back-ups of my library that are not synced to any cloud, on my PC and on two external HDs. But my "working" library is synced to Dropbox because it's the most convenient solution for me (I work with my library on both my PC and my Surface tablet, of course not at the same time). There is really no other option for such an arrangement. I tried with a flash drive, but that was terribly slow. And it's too bothersome to connect and disconnect the external disks to my computers several times a day. So it has to be Dropbox. I never run Dropbox and Calibre at the same time, nor do I run Dropbox on my PC and my Surface at the same time. One has to be careful.