war story: some USB flash memories are very slow

[D. Hugh Redelmeier]

| From: Lennart Sorensen <lsorense-1wCw9BSqJbv44Nm34jS7GywD8/FfD2ys at public.gmane.org>

| > I dded the image to a USB stick.  This seems to be the way you have to do 
| > it for this image.  The dd took 36 minutes for 4.6 GB.  That seems very 
| > slow to me.  That's about 20k / second.
| 
| By my calculations it is 2.1MB/second.  Still not great.

Oops.  Bad arithmetic.  Thanks.

The top speed I got was closer to 4 MB/second.  That seems to match
this review for the 4G version of this stick:
  <http://www.legitreviews.com/kingston-4gb-datatraveler-101-usb-flash-drive_994/2>

| From: William Park <opengeometry-FFYn/CNdgSA at public.gmane.org>

| 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?

Direct I/O is something like raw I/O in UNIX systems.

Raw I/O meant your I/O operations went directly to the device, without
going through the buffer cache.  It also meant that there was no or
little deblocking / blocking logic in between.

Flash memories only pretend to have 512-byte blocks.  If you write in
larger chunks, I can imagine that you cut down on bad side-effects of
this pretense.
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