On 2010-10-22, at 12:01, Lukas Czerner wrote: >> That patch also checks for the zeroing feature. When this patch was first under discussion, I proposed that we validate that the device is actually zeroed by doing a write a non-zero block to the disk and then calling discard+zero for that region, and reading back the block and verifying it. >> >> Eric wasn't convinced that was necessary, maybe you can convince him more... > > One of the counter arguments was, that some devices does not preserve > this behavior through power cycles. I think Ted was the one talking > about that. Sure, I don't think we can handle every pathology, but doing a write/discard/read of a few blocks (when it has the potential to avoid many GB of writes for zeroing) is surely easy and worthwhile? In any case, I thought that discussion was about a device that didn't report BLKDISCARDSZEROES=1, but only that a normal DISCARD would read back zero until the next restart? That prevents optimizations like "read until we see non-zero data, then start writing zeroes", which would still be faster for many RAID devices (or older kernels that don't have DISCARD/ZERO support at all). Cheers, Andreas -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
