What if you try copying from memory rather than dd if=/dev/zero?
It may be that when you boot from NAND it's automatically mounted in 'sync'
mode rather than 'async'.
AJ ONeal
On Mon, Sep 6, 2010 at 4:10 AM, Victor Andres <victor@...> wrote:
> From a Kingston 2GB class 4 on Overo, booted from the microSD card:
>
> root@...:~# dd if=/dev/zero of=/zero.dat bs=1M count=1000
> 1000+0 records in
> 1000+0 records out
> 1048576000 bytes (1.0 GB) copied, 236.848 s, 4.4 MB/s
>
> There's about 1.1 MB/s different with the result of your experience.
>
>
> But there's something that I don't understand, if I boot from NAND and run
> the same I get only 1.2 MB/s.
>
> root@...:~# dd if=/dev/zero of=/media/mmcblk0p1/zero.dat bs=1M count=1000
>
> 1000+0 records in
> 1000+0 records out
> 1048576000 bytes (1.0 GB) copied, 859.527 s, 1.2 MB/s
>
> Regards
>
>
> ----- Original Message -----
> *From:* Cole Christensen <chri2586@...>
> *To:* General mailing list for gumstix users.<gumstix-users@...>
> *Sent:* Friday, September 03, 2010 7:35 PM
> *Subject:* Re: [Gumstix-users] microSDHC write speed comparison
>
> AJ,
>
> I believe your test method is flawed.
>
> My results for a (generic) Class 4 MicroSD on Overo, booted from the SD
> card:
>
> root@...:/# dd if=/dev/zero of=/zero.dat bs=1M count=1000
> 1000+0 records in
> 1000+0 records out
> 1048576000 bytes (1.0 GB) copied, 190.283 s, 5.5 MB/s
>
> while your cat | dd is still reading from the disk, hence the slowdown.
>
> Yours is a test of copy speed, not pure write speed.
> I am not yet sure if my method is entirely valid either.
> Would transferring speed be artificially high when all the bits are zero?
>
> On Fri, Sep 3, 2010 at 11:13 AM, Robert Vogt IV <robert@...> wrote:
>
>> Hi Cole,
>>
>> Agreed. I have some numbers for various random number generators on a
>> 16-core Itanium (RHEL 4):
>>
>> Method Speed (MB/s) Speed (MB/s)
>> (saving data) (pure generation)
>> Urandom 4.19 4.61
>> System 39.67 250.94
>> Cran32 37.64 186.29
>> Lcg 29.16 72.98
>> Rtprng 40.17 276.17
>> Isaac 42.07 375.38
>> Sfmt 43.32 563.38
>> TR1-MT 29.66 83.17
>>
>> As you can see, urandom is by far the slowest, followed by random
>> (random blocks waiting for entropy if necessary, making it quite hard
>> to get lots of data). Of course, for write testing, one doesn't even
>> need random data...
>>
>>
>> Robert Vogt IV
>> CEO
>> IOSiX, LLC
>> 2375 Parkwood Ave
>> Ypsilanti, MI 48198
>> robert@...
>> P: 734-730-9690
>> F: 734-482-2337
>>
>>
>>
>> On Fri, Sep 3, 2010 at 4:49 AM, Cole Christensen <chri2586@...>
>> wrote:
>> >
>> >> root@...:~# dd if=/dev/urandom of=/media/mmcblk0p1/rand.dd bs=1M
>> >> count=100
>> >
>> > If your input is urandom the bottleneck could be the random number
>> generator
>> > and not the disk.
>> >
>> >>
>> >>
>> >>
>> >> ----- Original Message -----
>> >> From: AJ ONeal
>> >> To: General mailing list for gumstix users.
>> >> Sent: Friday, September 03, 2010 2:25 AM
>> >> Subject: [Gumstix-users] microSDHC write speed comparison
>> >> I'm testing out various brands and classes of microSDHC to see which
>> >> actually perform as they should and whether the microSDHC or the
>> gumstix
>> >> data bus is my write speed bottleneck.
>> >> http://fastr.github.com/articles/testing-file-write-speeds.html
>> >> So far I would recommend Kingston. It's more expensive, but it performs
>> >> well. I should have a class 10 of theirs soon to test against.
>> >> AJ ONeal
>> >>
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