I recently got a few (5) hard drives to turn my home server into a NAS with trueNAS scale and my idea is to have 4 usable and 1 for redundancy, my question is… How does RAID work, like what is RAID 0, RAID 5, software RAID etc, and does any of that even matter for my use case?
Other people gave a good explanation of raid and some alternatives like zfs in truenas.
You want to avoid RAID5 with drives above 4TB. Every hard drive has can have an unrecoverable read error (URE) during the read. It’s a very low percentage change that your hard drive publishes. During a raid 5 rebuild after replacing a drive, the other drives are stressed for a long time during the rebuild. With high capacity drives you have a pretty large chance of encountering a URE and losing the entire array. The high stress on the drives can also cause drive failure if another drive was on its way out.
I run truenas core at home in volumes that looks like raid 10. Two mirror volumes striped together for performance.
I never played around with raidz1 (like raid 5) but you still have the chance of an URE during the resilver. I can’t comment if it’s possible or what happens during an error. I did see people recommending raidz2 to allow for two disc failures from losing data during a resilver.
All my disks are 2TB so it shouldn’t be a massive issue
I personally wouldn’t use raidz1 because it seems too risky to me. I’d have higher redundancy.
Some links
https://www.truenas.com/community/threads/raidz1-vs-raid-5-ures.42598/
https://www.truenas.com/community/threads/5x-4tb-raidz1-array-rebuilding-with-nre-ure-issue.13719/
https://magj.github.io/raid-failure/
The last link is talking about actual raid and not zfs. But it has a 50/50 chance with a URE rate of 10^14 to lose the array. Raidz1 maybe won’t have that catastrophic of a failure, but you’d still be rolling the dice on some corruption.