Zero disks

[chripede]

When you add a new disk in unRAID you have to zero it first to make sure the xor isn't effected on the parity drive. I suppose you should do that with nonraid as well?

[qvr]

You don't really need to do preclearing with unRAID either, it seems people mostly do that to stress-test the disk beforehand.

nmdctl add will currently always add disk in a way that it will need to be cleared after the array start (the clear operation needs to be triggered with nmdctl check) - the disk won't be in use and won't affect parity calculations before it has been cleared.

Option to allow pre-cleared drives could be dangerous with nmdctl, the driver itself does not check whether the disk is actually cleared or not, and if it isn't, then it will cause parity issues.

In UnRAID as far as I've been able to dig, the UI checks some magical clear signature in specific sectors to determine if the drive is cleared, before actually passing it onto the array driver - not sure I'd want to add that to nmdctl.

[chripede]

You're right, you can add it without but I believe that triggers a parity rebuild.

Appreciate the info and the effort you're putting into this project 👍

[qvr]

Nope, it's not a parity rebuild, the driver will clear only the newly added disk (because it has been imported as not cleared), and the new disk will then join the array only once the clear is done.

[qvr]

If you want to add a drive without clearing it, then you can do the "new config" operation, ie. create the array configuration from scratch, that will by default then trigger a parity rebuild (but then you'd be without parity protection for the duration of the rebuild).

[chripede]

I was just skimming the readme and didn't really see much about clearing/zeroing, which is why I asked. Reading the cmd script makes things a little clearer.

[qvr]

That's a good point 👍
Added a few words about that:
#42