Raid1 actually gets you less than that. If you mirror 5 drives that only gives you 1 drive worth of data (with 4 redundancies). But… you have to weigh it again

Raid1 actually gets you less than that. If you mirror 5 drives that only gives you 1 drive worth of data (with 4 redundancies). But… you have to weigh it against losing all your data. With raid5 if any 2 of your disks die at the same time then you've lost your volume and most likely 100% of your data (no matter how many disks you have). With raid1 you have to lose _all_ your disks before that happens. Typically that's also just 2 but you can mirror 3 or more drives if you need some data to be _really_ resistant to disk failures and you don't care about "wasting" n-1 times the space. So you end up trading off efficiency of storage space and resiliency to data loss. Myself, disks got cheap enough that I always just buy 2 disks and mirror them. I find it easier to reason about overall, especially in the face of a degraded array.