Legato has a concept of backing up to a 'pool' of tapes - unless you are removing each day's tape to take offsite, it is OK to allow Legato to write again the next day on the same tape. If your daily backups are modest, it is possible that you could get 3, 4, 5 or more days onto a single tape.
Legato keeps track of it all and knows what backups are on what tape cartridge.
Tapes in a pool can be in the autochanger, or stored nearby- but they are still part of the pool.
When you do a data restore Legato will know what tape(s) to ask for... they need to be in the autochanager or close by so you can put them in there.
How many tapes you will need in your 'pool' will largely be determined by your browse and retention settings (read up in the docs for this) and, of course, how many systems, how often you do full backups, etc.
A tape volume will become eligible to be 'recycled' (overwritten) once every saveset on that tape has expired. These savesets expire based on your browse and retention settings. If you plan on (say) retaining data for a year, then you will need lots of tapes. If your retention is set much lower (a week or two) then you will need far fewer tapes.
Yes, Legato can be a bit daunting at first but once you understand its concepts (it took me a while of just playing with it and reading all of the docs) you will do just fine.
I suggest that you step back and not try to force Legato to 'do backups for you the way you always did', instead look at it as "For each system (client) that I need to back up, 1) how often do I need to do a backup 2) how often do I need to do full backups(*) 3) how long do I need to keep the data 'very handy' for a recovery and 4) how long do I need to keep the data before I can overwrite it."
(*) Full backup frequency just depends on how important it is to you to quickly recover your data. One extreme would be a full backup every day (or, with Legato, you could do it more often than that!), the other extreme would be (say) one full backup a month, and some kind of incremental scheme in between. The downside of infrequent full backups is the recovery time required if you would lose a disk that hadn't had a full backup performed for 30 days- a lot of tape jockeying just to get the data back to its most recent state.
Where I work we happen to do once-a-week full backups and incrementals on the other days. If you go longer than a week between full backups then I strongly suggest you study the numeric 'backup levels' and how to implement them. That may mean far fewer tape recoveries than my extreme example above of 1 Full + 30 incremetal restores.
