Theodore Tso wrote:
The fastest and probably most important thing to add is some readahead
smarts to directories --- both to the htree and non-htree cases. If
you're using some kind of b-tree structure, such as XFS does for
directories, preallocation doesn't help you much. Delayed allocation
can save you if your delayed allocator knows how to structure disk
blocks so that a btree-traversal is efficient, but I'm guessing the
biggest reason why we are losing is because we don't have sufficient
readahead. This also has the advantage that it will help without
needing to doing a backup/restore to improve layout.
Something I just thought of: ATA and SCSI hard disks do their own
read-ahead. Seeking all over the place to pick up bits of directory
will hurt even more with the disk reading and throwing away data (albeit
in its internal elevator and cache).
Jeff
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