MicroSD Card performance variance on XO-1.5
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
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.
One Laptop per Child (OLPC) Australia
p: +61 425 239 701
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...
> 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:
>> How to check your internal SD card brand & model:
>> 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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