I plan to travel by train to Sevilla from Granada and was curious how the luggage space is. I will have a large backpack that I used in college that I plan to travel with during my time in Spain. It was extremely convenient during my trip throughout Europe 10 years ago. I wasn't sure if the trains in Spain are different.
Will not be an issue.
'large' - how small is that?
It goes in the overhead, the end of the coach or between the seats storage.
Ample storage at the entrance of each train car...Have never seen anyone with a problem. Your ticket will have the car number and the seat number as well. There is limited security as you board. (X ray and perhaps open inspection.)
Spanish trains (whether fast or slow) are similar to their counterparts across Europe. Any bag that you can easily handle yourself will fit on the train; see also http://www.ricksteves.com/travel-tips/transportation/trains/on-the-train. Pask as lightly as possible, since you're the one who will be carrying it up and down stairs in hotels and train stations, etc.
LOL -- sure ample.
I nearly saw a trainful of Spanish travelers come to blows -- there was much shouting, tossing of other people's luggage and strutting -- on a trip from Granada to Madrid because there was nowhere near enough space at the end of the car for the luggage -- and some people with smaller cases refused to put them in overhead racks and those with large cases tried to force the issue by moving the smaller cases. We ended up with a good deal of luggage stacked in aisles.
If the backpack will fit in the overhead, which it may well do -- then you won't have a problem -- but the racks at the end are grossly inadequate if there are very many travelers with significant luggage.