war story: some USB flash memories are very slow

Tue Dec 10 21:43:43 UTC 2013

On Tue, Dec 10, 2013 at 03:39:39PM -0500, D. Hugh Redelmeier wrote:
> TL;DR:
> 
> When dding to a raw USB flash memory, you can save perhaps half the
> time by:
> 
> 1) using a reasonably sized buffer.  1M seems enough.
> 2) using direct I/O.
> 
> Example:
> 	dd if=Fedora-20-Beta-x86_64-DVD.iso of=/dev/sdi oflag=direct bs=16M && eject /dev/sdi

What is the meaning of "direct I/O" here?  This option gives me only 5%
improvement, ie.  12MB/s vs 13MB/s.  Shouldn't buffering give you better
performance?
-- 
William
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