he could write files and delete them, over and over, ad infinitum
True in some very rare cases:
E.g. If you write to SD cards (flash without wear leveling) and you have no disk cache, then you can wear out the card.
Not true if:
- If he does that with small files and the write does not even make it to the disk, just to the disk cache. Then it gets deleted before the actual flush happens.
- Not true for regular spinning HDDs. These already take that sort of abuse and happily live on for years. (After 6 years I consider replacing heavily used server disks, but they might work fine for another decade. By that time the hardware is technically outdated though).
- Not true for modern SSDs. The first generation had relative low write limits, but those are much higher on modern SSDs. The result is that a SSD is technically outdated again before hitting that limit. (Some tech site(s) even tested this by using a SSD in a desktop, writing to it 24/7 with a background task and then testing the SSD after a year. It was fine. If you have a user who does this for a year and you fail to detect that then the problem is not a technical one).
Lastly, it might hurt the performance of your system. If someone is hitting the disk IO all the time then less throughput will remain for the rest of the system.
Is this actually a risk, and if so, what can be done to prevent it?
No actual risk, but monitoring your systems is always a good idea. Not just for someone doing weird stuff, but also for a myriad of other cases, such as failed fans / high temperature, for failed drives (they do fail now and then, entirely on their own and with no abuse needed), failed RAM, ... ...