[clug] another rainy day time filler - CF reader

Paul Warren paul.warren at anu.edu.au
Sun Feb 14 16:07:32 MST 2010

Hash: SHA1

Eyal Lebedinsky wrote:
> I need a fast CF reader. My current readers read between 2MB/s and
> 16MB/s. My camera reads 16MB/s. I am testing a DickSmith own brand
> 33-in-1 that reads 25MB/s. All is over USB.
> I test copying a 1GB file then check the vmstat rate once it
> stabilises.
> Now the CF itself is speced at 60MB/s, so I want to reach the
> USB limit (40MB/s?) which is good enough for me.
> I know that I can go firewire or maybe even sata card reader,
> but I do not expect a significant benefit, especially when used
> to copy many smaller images (5-25MB each).
> Does anyone have a good solution, with personal experience?
> Or maybe 25MB/s is already a good result over USB?

I'm fairly sure that USB 2.0 has a maximum possible transfer rate of 480
megabits/s, which is 60 megabytes/s.  But that is only the trasfer rate
for the USB transport.  USB protocol overheads take a significant whack
out of that, and there are fairly large delays between packets also.
- From my experience, the most you're going to get out of a USB connection
is 25 megabytes/s of actual data transferred.

It sucks, but that's the way it is. I have a disk in a caddy that does
both eSATA and USB 2.0, USB 2.0 gets ~24 MB/s and eSATA gets ~40MB/s. I
haven't tried it without the caddy and straight into SATA, but I'd
imagine it'd be roughly the same as eSATA.

- --
Paul Warren
ARCS System and Data Services
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