Requesting advice/ recommendations for steps forward. Is the NAS cooked? Could I upgrade the drives and still get some life out of it?. How likely is it just a single bay (not the disk) failed on the nas?

All of the system was bought second hand about 2 years ago but factory wiped. Drives look like they've got 4-5 years runtime on them before I bought it.

I've got a 4 bay nas it has 4x3TB drives in it. A few days ago there was an issue with Bay 1 where it lost sync or something. I pulled it out and put it back in and removed it from the volume and re initialized it and it came up good.

Yesterday the light for bay 1 didn't come on and system showed as degraded.

I tried to fault find by swapping the disks in bays 1 and 2. And I think it gave light on bay 1 but am not sure. I'm not in a position to try again as priority 1 is to make a copy of all data on the nas as-is.

When I put everything back as it was bay 2 came up with a partition error, so I stopped fault finding and started data copying.

My plan is to remove all data and then fault find to see if drive of bay is the issue and then possibly re initialized a volume with bays 2-4 as raid 5. But there's part of me saying once a failure has occurred there's likely to be a second one soon.

Edit: I also got a warning about increased fan noise but it didn't sound louder to me.

Thanks in advance.