• The ntfs-3g programme accesses the NTFS volume's block device (/dev/diskN) and performs I/O on it. When block devices are accessed in this fashion, Mac OS X does not have a VM buffer cache. Because all metadata operations and file data I/O boil down to ntfs-3g read/writes to the block device, this is the most overpowering aspect.
• Assume we were able to implement uniform buffer caching for block devices by effectively turning a disc into a large file. Even so, OS X and its buffer cache are only pleased when you do I/O in page size (4KB) units that is aligned on a page boundary. ntfs-3g (or any other programme for that matter) would want to do I/O in multiples of 4KB to get the most out of OS X's I/O subsystem.
• Try writing to an NTFS disc image as a comparison; you'll notice that it's much faster because there's some cache in that scenario. There are versions of ntfs-3g that have additional user-space caching, which improves performance significantly.

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