Thank you all! Now I understood my expectation was wrong. My goal is to erase the existing filesystem's data on RBD. I'll use `blkdiscard -z` or `ioctl(BLKZEROOUT)`. # To Anthony: > My sense is that blkdiscard is intended for something different from what you’re intending. I understood, thanks. I thought discard implies zero-filling. > Was there a mounted filesystem when you ran the below? Yes, there was a filesystem. My goal was to zero-out its data. # To Slava: > Could you confirm that it worked as you "expect" before 6.6.95? Otherwise, it's not the issue or bug. I just tried that commands in 6.6.95 and my expectation was wrong as described before. So the behavior that I reported isn't a bug. # To Ilya: > This isn't really specific to RBD. If you want to efficiently zero a given range, use BLKZEROOUT (pass -z to blkdiscard command). Thank you for letting me know. I'll use it. I verified it's far faster than filling zeroes by `dd`. Best, Satoru
