On Feb 29, 2012, at 2:12 AM, Lukas Czerner wrote:

The reason is (as I commented in the patch #2) that we will not discard
BLOCK_UNINIT groups. We use BLOCK_UNINIT as a optimization measure to
skip groups which are likely to be non-provisioned, because we have
never written there anything since the mkfs.

If you create file system without discard, then obviously nothing is
discarded, image is fully provisioned and e2fsck discard *only* initialized
groups. So you'll end up with the bigger image, in case that your image was
not sparse.

i still think it makes sense to have an option where we discard everything
including BLOCK_UNINIT blocks.   Mke2fs doesn't discard blocks by default
because of a fear of crappy SSD drives, and while that fear may be
overstated, assuming that all of the unused blocks will *always* have been
discarded at mkfs time isn't necessarily a good thing to assume.   I'll grant
that it might be a fine default, but there needs to be *some* way to discard
everything that's unused….

-- Ted

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