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#1 (**permalink**) 02-16-2008, 05:07 AM

All:

I am trying to build a compact flash based system and am worried about how
slow the compact flash drive is writing. I built my disk image and am in
the process of copying over the disk image to the compact flash.

Using:

dd if=disk.image of=/dev/rwd1c bs=512

I am achieving a transfer rate of about 120,000 bytes per second. My 512
megabyte compact flash will therefore take over an hour to copy over the
disk image.

I tested dd sending the file to /dev/null to see if it was dd:

dd if=disk.image of=/dev/null bs=512

This command achieved a transfer rate of 14,000,000+ bytes per second.

I am using a Kingston 512 mb compact flash card and expected transfer rates
in the 2,000,000 bytes per second range from reading stated read and write
transfer speeds for this card.

Ass-u-ming that this card is good, does anyone have any thoughts on why the
transfer is so slow using dd and OpenBSD? Anyone else run into this
problem? Is there a tweak I need to set for using CF cards with OpenBSD?
My concern is that this card will also be slow when reading, which would not
be acceptable.

TIA,

Jim

#2 (**permalink**) 02-16-2008, 05:07 AM

On Fri, 26 Dec 2003, Jim Lambert wrote:

> dd if=disk.image of=/dev/rwd1c bs=512
>
> I am achieving a transfer rate of about 120,000 bytes per second. My 512
> megabyte compact flash will therefore take over an hour to copy over the
> disk image.

a larger block size of 16k will probably be faster. i wouldn't expect it
to be too fast, though reads should be faster. if your application calls
for reading 512M of data regularly, maybe compact flash isn't the best
solution. most people i know using compact flash only boot from it, and
rarely touch it after.

--
"First, it was not a strip bar, it was an erotic club. And second,
what can I say? I'm a night owl."
- M. Barry, Mayor of Washington, DC

#3 (**permalink**) 02-16-2008, 05:08 AM

"Ted Unangst" <tedu@stanford.edu> wrote in message
news:Pine.GSO.4.44.0312261841470.15318-100000@elaine20.Stanford.EDU...
> On Fri, 26 Dec 2003, Jim Lambert wrote:
>
> > dd if=disk.image of=/dev/rwd1c bs=512
> >
> > I am achieving a transfer rate of about 120,000 bytes per second. My
512
> > megabyte compact flash will therefore take over an hour to copy over the
> > disk image.
>
> a larger block size of 16k will probably be faster. i wouldn't expect it
> to be too fast, though reads should be faster. if your application calls
> for reading 512M of data regularly, maybe compact flash isn't the best
> solution. most people i know using compact flash only boot from it, and
> rarely touch it after.

The 512 M size is only because I thought I needed that much. I have since
seen that I don't need that much. I am just booting off of the compact
flash and starting a couple of programs.

As for the block size, can I make it 16 k without messing up the disk image?
I'm new at writing disk images directly to disk and am not sure what making
the block size 16k will do.

TIA,

Jim

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Compact Flash writing slow?