What do these Copy Only Backup options mean?
It's a full dump of a database, where you intent to take that dump and load it into some OTHER sql server instance. e.g. It's a nice way of making a complete copy of a DB without having to take down the db, detach the db, copy the .mdf files, re-attach, etc...
Naturally, since you're not using this "backup" as an actual backup, you don't want it to interfere with your normal backup schedules, hence the copy-only functionality. It's a full backup, but will not reset the backup schedule, so your normal next incremental/snapshot backup will work as usual.
This mechanism is necessary since the built-in hotcopy/migration tools in MSSMS are basically useless and can't handle its own databases in many cases.
Normally when you take a backup, it starts (or continues, depending on the type of backup that you took) what is called a log chain. Let's say that you need a copy of your database and, for whatever reason, you can't use your normally scheduled backups for this purpose. Let's walk through the scenario where you don't use a copy_only backup
- Normal full backup
- A bunch of differential backups
- Another full backup (to make your copy database)
- More differential backups
- Delete the backup from step 3 (you know... to save space)
- Disaster on your actual database that necessitates restore from backup
In this case, you can only restore to the last differential backup made in step 2 because the differential backups made in step 4 depend on the full backup from step 3. Now, if the backup in step 3 were a copy_only backup, you'd be fine because you're not re-establishing a log chain (which is to say that the differential backups in step 4 depend on the full backup from step 1.