Empty volumes are not empty. Except data there's also a metadata (hash sums, changed block bitmaps and so on). All of these things need to be verified and synced. Just ASSUMING empty volumes are identical is dangerous.
Dangerous? In what way? It one was playing around at block level, then yes I could see that the mirrors contained differing data then there could be a problem but I'm struggling to think of one.
You don't worry about the content when you create a flat IMG in non-clustered world - when you create those, a (say) 1TB file is created instantly. You don't zero it out. In a situation like that, what does the OS get back if it reads a random block? I assume the random garbage that was on the disk before. Is that dangerous? Not really as if you read random blocks, you expect to get random data.
Okay with a mirror system that was left with the random data in there, you'd get different random data if you read the same block twice and the first time it from one node and the next time from the other node. But what OS reads random blocks? The first thing you do is format the disk so that the data is in a known state by writing the empty file structure.
Are you saying that fast-initialization of RAID arrays is dangerous? Because I'd estimate 99% of arrays are created that way and it's a very similar discussion. I'm not that familiar with RAID controllers to know whether fast initialisation allows the mirror to be used immediately but then mirrors the blocks in the background. Possible but never seen that on a RAID user interface.
So please consider fast synchronisation. Give me the choice. Sure, I know other stuff needs to be mirrored across but not the entire 32TB disk...
Cheers, Rob.
