SHA question

Philip Newton philip.newton at
Thu Jan 14 13:02:51 GMT 2010

On Thu, Jan 14, 2010 at 13:22, Peter Corlett <abuse at> wrote:
> For de-duping purposes, SHA is still faster than you can pull the files off the disk and a secondary cheaper hash is unnecessary.

That reminds me of how I was disappointed to find that rsync generally
transfers complete files (rather than diffs) if both source and
destination are on a local file system -- before I realised that to
compute the diffs, it would have to read the entire first and second
files, and if it's going to read the entire first file from disk
anyway, it can simply dump it over the second file without checking.
Computing diffs would be more work in this case, not less.

So yes, I suppose something similar applies here -- you have to read
the entire file anyway, so you might as well go with

Philip Newton <philip.newton at>

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