On Fri, 22 Oct 2010, Andreas Dilger wrote: > On 2010-10-22, at 08:46, Ric Wheeler wrote: > > On 10/22/2010 10:32 AM, Lukas Czerner wrote: > >> > >> Also there is a big win, when discard > >> also zeroes data, because in that case we can just skip inode table > >> initialization (zeroing) without any need of in-kernel lazyinit code > >> enabled. And we get all this for free. It was introduced with Sandeens > >> patch: > >> > >> http://marc.info/?l=linux-ext4&m=128234048208327&w=2 > >> > >> So, I would rather leave it on by default. > > > > You cannot 100% depend on discard zeroing blocks - that is not a universal requirement of devices that support it. Specifically, for ATA devices, I think that there are optional bits that specify how a device will behave when you read from a trimmed region. > > 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... > > Cheers, Andreas 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. -Lukas -- 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
