I am experimenting with setting up a raid with different size drives.

Here are my drives
sda 300GB
sdb 150GB
sdc 300GB

What I want to do is create 150GB partitions on all the drives so
sda1 150GB
sda2 150GB
sdb1 150GB
sdc1 150GB
sdc2 150GB

I would then set up raid 5 with 2 drives for redundancy.

Will this work?

If I create an array with 4 drives and 1 spare, is the spare active? so that if one of my 300GB drive dies will it still work or are the spares just sitting there with no parity info on them at all until they are needed. If so, is there a way to make spare active?

Well, technically, it should 'work' since each partition can be read as a separate device. But in practice, you actually need separate drives because if one of your 300Gb drives crash, then both partitions are lost which would defeat the object of having spare drives in the first place.

Ya, I have been running some tests and it seems like the spares are just sitting there doing nothing until they are needed.

I could use raid 6 and I think it would work in this example since then if my 300GB fails the array would still be live since raid 6 has 2 parity drives. But I still have to test this example.

But is there any way to make the raid have more parity drives? I have searched and I can see zfs allows for triple parity, but can't see anything for mbadm, or even allowing for n parity.