If it’s just steam you can limit your download speed. But 100Mbps is already pretty slow. Is your SSD throttling or failing? Or is the non cache write speed just really that bad?

you can try changing your io scheduler: https://wiki.archlinux.org/title/Improving_performance#Input/output_schedulers

i think by default ssd and nvme drives get ‘none’ as they should be fast enough to just take first come first serve and get everything done, however in certain cases like this you can get bogged down by a single thing hogging the drive for a long time. i’d recommend ‘kyber’, it’ll treat io requests similar to network requests and give requests tokens that ensure everything requesting io gets the io within reasonably responsive timeframes. note: this will slow your single task read/write speed, but only a tiny bit and it’s worth it for other things being able to use disk while it’s being hogged like on a game update.

Did you check memory usage at the same time? Install would certainly be IO intensive but probably shouldn’t max out a decent nvme drive.

If you ran out of ram due to the games installer and you started swapping that could quickly max out IO and DEs tend to stall quickly when the system is short on ram which also matches your symptoms.

There’s a command called ionice that does what you’re looking for.

I had this happen shortly before I had an SSD failure. How old is the drive? Check the SMART health if the drive is capable.

Have you tried to limit the download speed? Steam needs to write the downloaded data on the disk. If it downloads less, it should write less.

The ionice command might work for you here.