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Date: Wed, 29 Feb 2012 23:47:51 -0500 From: Theodore Tso <tytso@....EDU> To: Lukas Czerner <lczerner@...hat.com> Cc: Theodore Tso <tytso@....edu>, Eric Sandeen <sandeen@...hat.com>, ext4 development <linux-ext4@...r.kernel.org> Subject: Re: mkfs.ext4 vs. e2fsck discard oddities 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 -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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