MicroSD Card performance variance on XO-1.5

John Watlington wad at laptop.org
Wed Aug 18 11:23:59 EDT 2010

Buy a C6 card and test it out!   Applications load faster, boot time is
reduced, any file I/O completes faster, and your pictures are
more colorful!   (Just kidding about the last one.)

At the same time, outside of recording higher resolution video
a laptop with a C2 card is fully functional.


On Aug 18, 2010, at 6:13 AM, Sridhar Dhanapalan wrote:

> 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.
> Thanks,
> Sridhar
> 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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