What makes this different from regular md? I'm not familiar with unRAID.
replies(2):
- It lets you throw JBODs (of ANY size) and you can create a "RAID" over them.
- The biggest drive must be a parity drive(s).
- N parity = surviving N drive failures.
- You can expand your storage pool 1 drive at a time. You need to recalculate parity for the full array.
The actual data is spread across drives. If a drive fails, you rebuild it from the parity. This is another implementation (using MergerFS + SnapRAID) https://perfectmediaserver.com/02-tech-stack/snapraid/
It's a very simple model to think of compared to something like ZFS. You can add/remove capacity AND protection as you go.
Its perf is significantly less than ZFS of course.
But if the file system is corrupt then you're hosed and end up with a `lost+found`. It sounds great until it fails, and then you realize why ZFS with replication makes sense. Unraid doesn't do automatic repairs from replicated ZFS datasets yet either even if you use individual ZFS disks within your Unraid array.