Backup questions

Backup questions

HI
I plan on doing an upgrade to the latest version this weekend. Is the SDP internal backup that runs every night the exact same as the one that is invoked as part of the update package? 

If I have a backup from the night before - I could skip the backup in the upgrade package because it is the same as the backup I already have?

I have 75G of service desk attachments on the file system but only 25G of free space. Does the backup actually backup the attachment files themselves and then compress them - or are you primarily backing up the DB with file pointers to the attachments?