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From: x0054 on 21 Apr 2008 21:04
I am having issues with compact flash card that I got. I is writing very
slow. It's a 32gb, 233x card. The read speed is unbelievable, but the write
speed is less then 1mb/s. What's wrong? It supposed to get at least 20mb/s.

- Bogdan
From: M.I.5� on 22 Apr 2008 02:58

"x0054" <x0054(a)index.com> wrote in message
news:Xns9A87B7CAAD4ABx0054indexcom(a)yourdomain.com...
>I am having issues with compact flash card that I got. I is writing very
> slow. It's a 32gb, 233x card. The read speed is unbelievable, but the
> write
> speed is less then 1mb/s. What's wrong? It supposed to get at least
> 20mb/s.
>

The first thing to note is that the write speed is always lower than the
read speed. This is due to the way FLASH memory actually does its writing.
Whenever you write anything, even if its only one byte, an entire block of
the memory is copied in to a buffer, the data altered as required, the
target block erased, the buffer then written to it and the block journal
updated to show where the block actually is (which requires another block
read, erase and write cycle). As you can appreciate this takes much longer
than just a simple read with the last six parts taking the longest. The
larger sizes of memory are generally made up from memory cells which are
much faster than their earlier counterparts, but a problem arises if the
card reader doesn't fully understand the architecture that some of the
larger sizes use or indeed their speed, and can introduce a bottle neck in
the data flow. This will certainly be the case if you FLASH memory reader
is more than a year or two old.

There is also a considerable amount of counterfeit memory out in the wild
that although marked as some of the larger sizes and reports itself as that
larger size, is in fact much much smaller (and much much slower). The
larger sizes are prime targets as they command the premium prices.


From: Mark F on 22 Apr 2008 18:25
On Tue, 22 Apr 2008 07:58:18 +0100, "M.I.5�"
<no.one(a)no.where.NO_SPAM.co.uk> wrote:

>
> "x0054" <x0054(a)index.com> wrote in message
> news:Xns9A87B7CAAD4ABx0054indexcom(a)yourdomain.com...
> >I am having issues with compact flash card that I got. I is writing very
> > slow. It's a 32gb, 233x card. The read speed is unbelievable, but the
> > write
> > speed is less then 1mb/s. What's wrong? It supposed to get at least
> > 20mb/s.
> >
>
> The first thing to note is that the write speed is always lower than the
> read speed. This is due to the way FLASH memory actually does its writing.
> Whenever you write anything, even if its only one byte, an entire block of
> the memory is copied in to a buffer, the data altered as required, the
> target block erased, the buffer then written to it and the block journal
> updated to show where the block actually is (which requires another block
> read, erase and write cycle). As you can appreciate this takes much longer
> than just a simple read with the last six parts taking the longest. The
> larger sizes of memory are generally made up from memory cells which are
> much faster than their earlier counterparts, but a problem arises if the
> card reader doesn't fully understand the architecture that some of the
> larger sizes use or indeed their speed, and can introduce a bottle neck in
> the data flow. This will certainly be the case if you FLASH memory reader
> is more than a year or two old.
What you say is true, so the issue is how can the original poster get
close to the published speed specification. The techniques I use
include:
.. writing large files that are allocated in one step. If your program
doesn't allocate in one step, try sending the output to a hard disk
and then copy the full file to the flash memory. Speeds up some
backup programs by a factor of 100 or more since even though the
program has a good estimate of the total size needed it allocates
space in very small pieces.
.. use VMware or some other virtual disk software to put container
files for a virtual disk on the flash memory key and write to
the flash memory key through the virtual disk interface.
>
> There is also a considerable amount of counterfeit memory out in the wild
> that although marked as some of the larger sizes and reports itself as that
> larger size, is in fact much much smaller (and much much slower). The
> larger sizes are prime targets as they command the premium prices.
>
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