I need to first say I have no experience with that burn in software, so I can’t give any advice specific to that. With that being said it could be a few things. Obviously the drive could be bad, but it appears to have zero errors indicated so far. If these are shucked drives, it is possible that the one drive is a different model. When brands make external hard drives they will use multiple models, it is possible that 7 are a higher class model and the slower one is a lower class or otherwise different. Again I’m not familiar with the software, maybe something weird is going on with it and it is hitting that drive less. You might have an old or damaged sata cable that isn’t allowing it to achieve full 6 gb connection. Some motherboards can have wonky setups with their sata controllers, maybe something is going on with that sata port.

I’d allow the test to complete, if it has errors then you know it is likely bad. Do a speed test, if it is noticeably different then try switching the sata cable from one drive to another to see if the problem follows the cable / port. Make sure all drives are formatted the same, maybe something funky happened with the formatting or the test runs different with different formats. I’d also check the drives with a different software like crystaldiskinfo and see what it says. It can tell you the rpm of the drive, firmware version, if there are any smart errors and more.

I have about 45 tb worth of data, mainly movies, tv shows, and roms. I have an unraid server that I use for daily use. The Unraid server has a single parity disk in the event of disk failure. For redundancy I also use external hard drives for cold local storage, they get updated about once a month. Lastly I have a friend who lives in another town whom I have all my data backed up with, and I backup his data as well. We backup each other’s data around twice a year. Lastly I have about 20 gigs of data which I really don’t want to lose, I have this data backed up to the cloud as well.

With that being said to me it is just a matter of how important you think the data is, and what you feel comfortable spending to make sure you keep it. For me I’ve been data hoarding for about the last 10 years, so to me this is 10 years worth of work, and I’d rather not lose it.

To answer your first question about raid, I don’t consider it enough to satisfy the part 2 rule. For my server I bought all my hard drives at the same time. That means if they were a bad batch of hard drives they might all fail one after another. Even if I got a good batch, they are all getting used at about the same rate, so they will likely age at about the same rate. If one of the hard drives dies, the others are likely not far behind, and the stress of rebuilding the array might kill off the rest.

As to your second question, I try to limit how much I have stored on the cloud. For me it makes much more sense, if you want to have a third copy of your data, to buy an external hard drive and give it to a friend to hold onto.

I’d suggest doing what you have already done and continue to try different OS to find the one you are most comfortable with, and has the features you want. Personally I have used Unraid for about the last year. My experience with it has overall been positive, but there has been several times I’ve been left scratching my head as to why something is set up how it is. For example, I have a 1 tb cache drive for my array. I’d expect if I tried to transfer over more data than the cache can handle that after the cahce filled up the data I’m transferring would automatically fallback to transferring directly to the hard drive array. Instead if I try to transfer more than 1 tb the transfer errors out. After looking into it the general consensus is to disable the cache drive for large transfers, which is annoying.