It is vitally important that you protect all the work you have put into developing your Mendeley library. If you lose your Mendeley library it could delay your study or, possibly even cause you to fail.
Mendeley Desktop is fully synchronised with Mendeley Web whenever you are connected to the internet. Your references will be stored in the cloud.
For complete security and, when working offline, you should also make a backup of your Mendeley library. This will gather all the various parts of your library and compress them into a single .zip file. This file should be stored in a physically separate place to your computer.
To create a .zip backup file click on the Help pull down menu and then on Create Backup