MicroSD Card performance variance on XO-1.5

Sridhar Dhanapalan sridhar at laptop.org.au
Wed Aug 18 06:13:45 EDT 2010

I am trying to determine whether it is worth us spending this
additional $2-3USD.

Has anyone tested what the practical difference is when using a C6
card over a C2? Being able to record at high-res is a good start. What
about general speed and latency for normal use?

I took a look at the SD and USB FLASH Drive Performance wiki page, but
it isn't clear what the real difference is for classes.


Sridhar Dhanapalan
Technical Manager
One Laptop per Child (OLPC) Australia
p: +61 425 239 701
w: http://laptop.org.au

On 6 August 2010 09:55, John Watlington <wad at laptop.org> wrote:
> Early prototypes are built using a wide range of SD cards: I believe
> we used at least six models in B/C test machines.
> While individual developers usually only have one or two, we
> do make sure that all SKUs are distributed to some software
> developers and testers.   Both Quanta and the hardware team
> are careful to test across all prototype SKUs.   When we had a
> QA department, they too were testing on all SKUs.
> We could place C2 cards in all prototype SKUs, but then Quanta
> would refuse to use C6 cards without further testing.
> I've said it before, and I'll say it again.   If you want C6 cards,
> you will have to pay to get them.    OLPCA pushes Quanta
> for the lowest price, and C2 cards are usually $2-$3 cheaper
> than C6.
> BTW, the REAL definition of C2 versus C6 is the resolution
> of video that can be streamed onto the card.   So our higher
> resolution video encoding problems using C2 cards shouldn't
> be surprising...
> wad
> On Aug 5, 2010, at 2:54 PM, Martin Langhoff wrote:
>> We recently saw that (at least some) XO-1.5 developer machines (C1,
>> "ramp" units, etc) have SD cards that are significantly faster than
>> what is being shipped to end users.
>> This was a surprise to me (and probably to a few more of us) -- we
>> assumed that most dev machines had a similarly spec'ed SD card to the
>> shipping machines. AIUI, we intended to have an assortment of
>> "candidate" SD cards on the ramp units, the units I've seen all have
>> pretty fast cards :-)
>> This probably explains the scattered results of testing Record
>> audio/video sync -- with lots of 'works for me' vs "definitely doesn't
>> work". The slower SD cards are significantly slower.
>> Deployments can request faster cards (at a cost), but I think it makes
>> sense to test with the lowest common denominator. And we definitely
>> need to understand what SD card is behind each "works" or "doesn't"
>> report re Record and other write-intensive tasks.
>> To aid clarity, Mitch has added a ".speed" test to OFW -- and we've
>> timed a few cards with it:
>> http://wiki.laptop.org/go/SD_and_USB_FLASH_Drive_Performance
>> How to check your internal SD card brand & model:
>> http://wiki.laptop.org/go/XO_Debugging_tips
>> cheers,
>> m
>> --
>>  martin.langhoff at gmail.com
>>  martin at laptop.org -- School Server Architect
>>  - ask interesting questions
>>  - don't get distracted with shiny stuff  - working code first
>>  - http://wiki.laptop.org/go/User:Martinlanghoff
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