Image conversion and Inode usage
This question has been flagged as irrelevant so I guess this has no real worth to anyone so I tried removing the question but the system won't let me so I am now truncating the content of this post ;)
I think you need to run the actual numbers for both scenarios:
On the fly
- how long does one image take to generate and do you want the client to wait that long
- do you need to pay by cpu utilization, number of CPUs etc. and what will this cost for X images thumbnailed Y times over 1 year
- how much space will this use and what will it cost
- how many files are there? Is the number bigger than the number of inodes in the destination file system, or is the total estimated size bigger than the file system
It^s mostly an economics question, there is no general yes/no answer. When in doubt, I'd probably go with storing them since it's a computation intensive tasks and it's not very efficient to do it over and over again. You could also do a hybrid solution like generate a thumbnail on the fly when it is first requested, then cache it until it wasn't used for certain a number of days.
TL;DR: number of inodes is probably your least concern.