Back during the dot-com era, we lost an array to the "Deathstar" drives. They were all from the same production batch (we bought them at the same time). So when one died the others were not far behind. It was actually comical, in a sick & sad way. When the first drive died, we tell the data center tech to go replace it. But before he could walk over to our cage with the replacement, the second drive died. We tell him to run. And then the third drive died and the data was toast.

I have also only ever had problems with RAID 5. Many years ago, we ran a hardware RAID 5 and it was really very slow. I eventually bought some extra drives and switched to RAID 0+1 with much greater results and comparable availability.

If you can afford to purchase 2x the disks for RAID10 you will certainly get better performance and availability. RAID5 is an approach that gives you lower cost in return for slower writes and less fault tolerance. Everything is a trade-off.

definitely true - but it's really hard to gauge what performance will actually be until you have the whole thing setup even with benchmarks.

RAID 0+1, is that the same thing as RAID 10?

Nope... RAID 10 or RAID 1+0 is 2 or more RAID 1's that are RAID 0'd together

RAID 01 is 2 or more RAID 0's that are RAID 1'd together

yea I had a mirror of striped drives. Gave you max throughput with some protection against failure.

This article explains the difference in more details https://muetsch.io/why-raid-10-is-better-than-raid-01.html

RAID 10 works by stacking pairs of disks, as many pairs as you want, each pair is redundant by nature. It's common to do with 8 or 12 disks, filling the whole front bay of the server. It can survive many drives failing as long as it's not two drives from the same pair.

RAID 01 splits data differently. It's much more likely to lose the whole array if you lose any 2 disks, or god forbids, 3 disks.

RAID 10 is the proper level. RAID 01 is dead and almost nothing supports it, it's most likely a mistake or a typo if you heard about it used in production.

Our primary concern was absolute maximum performance on huge numbers of tiny files (terabytes of video cut into single-frame TIFFs) for video processing while also having at least some protection against a single failed drive. We were on a shoestring budget, so we couldn't upgrade our network to use fiber, so a SAN wasn't really feasible at the speeds we needed (SSD's also didn't exist yet). You could be right, but I know that I chose the one with the fastest possible performance and made sure there was an audible alarm if a disk failed.

No, my array was fine and all drives were fine, except that one drive that was affected by a lot of bad sectors.

The scrub did exactly what it was supposed to do. Because the drive seemed fine but it was not. It would have killed my array if any of the other drives would have failed.

This sounds to me like: "It was really one inch away from losing all the data"

You discovered the failing disk by chance; if chance hadn't been in your favour it would be the other way round and an other drive had failed on you.

No, I think you misunderstand: read about the scrubs, they run weekly or monthly. Nothing accidental about that.

I keep my server off most of the time. And that is a nice way of missing scrubs. In my case the scrub did what it needs to do: find disks with bad sectors. I should do something extra in the future to run scrubs if they miss their schedule.

RAID 5 is a reasonable way to add redundancy to three or (worse) four drives, sourced from different batches (or vendors).

Sometimes it's all you can afford, or could until ZFS became available for Linux.

For bigger setups, definitely other schemes are better.