RAID-10 (stripe of mirrors) is also an alternative.

Not as cost efficient, but rebuild times should be much lower. Is also more flexible in some cases, like when using ZFS for example.

Raid-6+ (16, 60, 100, etc), Raid-z2+ (raid-z1 being the equiv of raid-5), Ceph, etc

OK, good to know. So the process of rebuilding after having lost a disk will take less time with those other solutions?

It's not about the process taking less time (even though aiming to reduce that is a valid approach, which is usually tackled by using ssd/flash and not over-provisioning). It's much more about being able to handle a second disk failure during rebuild. With raid 5, if that happens, you are in a world of hurt (think 3k fees to send raid to data recovery place).

I've learnt all this the hard way.

Ah, makes sense. Thanks!

RAID 6 (adds an extra parity disk) or generalized erasure coding (more flexible but not so easy to manage).

Nitpick: RAID-5 and RAID-6 don't use "parity disks". They stripe the parity across every disk, just like RAID-0 stripes data, so you lose a disk worth of capacity (or two disks worth of capacity in RAID-6), but the parity is on every disk. Having a disk dedicated to parity would be an incredibly burdensome write bottleneck, which is exactly what RAID-4 is, and why you probably haven't heard of it.

I still use RAID 5 for small 3/4-disk arrays; I think the odds are in my favor then. But if I need 4x disk size, I go to RAID 6 (so I jump from a 4-disk RAID 5 to a 6-disk RAID 6.)

ZRAID1 oder ZRAID2

RAID 6