Any restrictions or recommendations regarding SD cards?

Thu Mar 24 20:27:47 EDT 2011

Hi Christoph:

Then is not so much a matter of I/O, at least not in the terms that we think
of it.

We're more incline to think how fast a file can be copied from the NAND to
the external device, but that only happens when you're copying several files
at once. We're programmers, geeks. Perhaps it does matter the first time,
when the index is created.

But thinking of the normal uses of a SD card, it would be hypothetically
always inserted to the laptop, and yet the kids are manually going to
transfer files, and that is as fast as our hands make it. "Righ click,
select option, transafer, done". Not a fast as the device can go.

I must admit that I'm not very current with OLPC knowledge, I've been
disconnected . But files cannot be trasfered in batches
And what would be the real case scenario for it, to free disk space, then is
not a matter of "how fast" but of "how much". The other case scenario would
be to share files, in which case it doesn't matter that much either.

If the OS is not running from the SD, I wouldn't worry that much about a
certain brand or speed. I could be more concerned about long term usage,
quality, lets call it life-span (http://goo.gl/yt6cE).

Now if you know that certain SD card cannot work as external drives, because
of a bug or something, then, you should not use those, but i have a very old
microSD card for about 3 years and works just fine to make backups, or to
transfer files to other machines. I even have soas in it, and use it every
once in while. Sometimes we just get lucky.

You should try different types and brands, as long as they all have the same
size, cause, in this cases, size does matter. This way if there is
statistics that proves one brand not working is minimal compared to the
whole batch of a bad brand.

I hope that makes sense.. :)

R

2011/3/24 Christoph Derndorfer <christoph.derndorfer at gmail.com>

> Hi Rodolfo,
>
> I think the idea is to use it as a storage device.
>
> Christoph
>
>
> On Fri, Mar 25, 2011 at 12:56 AM, Rodolfo D. Arce S. <
> rodolfo.arce.s at gmail.com> wrote:
>
>> Christoph:
>>
>> You're talking about running the OS from the card?
>>
>> Because you could use it as an external drive only. But I'm gessing that
>> if you take I/O into account you're going for the first option
>>
>> R
>>
>>
>> 2011/3/24 Christoph Derndorfer <christoph.derndorfer at gmail.com>
>>
>>> Scott, Arnd,
>>>
>>> thanks a lot for your comments and suggestions, much appreciated! :-)
>>>
>>> Cheers,
>>> Christoph
>>>
>>> On Thu, Mar 24, 2011 at 10:36 PM, Arnd Bergmann <arnd at arndb.de> wrote:
>>>
>>>> On Thursday 24 March 2011 20:26:05 Christoph Derndorfer wrote:
>>>> > Hi all,
>>>> >
>>>> > the folks from the Austrian pilot project want to equip the XO-1s
>>>> there with
>>>> > SD cards. Are there any restrictions wrt size, speed, etc. that they
>>>> should
>>>> > be aware of when purchasing the SD cards? I'm particularly asking
>>>> after
>>>> > reading James' mention of seeing more issues with newer cards and the
>>>> XO-1
>>>> > power off bug.
>>>> >
>>>> > Or asked the other way 'round: Are there any particular cards or
>>>> > manufacturers which people can recommend?
>>>>
>>>> Have a look at my list at
>>>> https://wiki.linaro.org/WorkingGroups/KernelConsolidation/Projects/FlashCardSurvey
>>>>
>>>> Stay away from brands that typically have only one writable allocation
>>>> unit, these will be slow and wear out very quickly when formatted with
>>>> ext3
>>>> or other Linux file systems. Higher is better here, and it's something
>>>> that
>>>> is usually not reflected in the speed class rating. Also avoid those
>>>> that only
>>>> support linear I/O.
>>>>
>>>> Sandisk cards tend to be ok (especially the Ultra and Extreme versions),
>>>> Kingston tends to be really bad, most others have somewhat mixed results
>>>> though sometimes the cheapest ones can be really good.
>>>>
>>>> Class 10 cards are not required to support efficient random I/O, so they
>>>> are
>>>> sometimes slower than Class 6 cards from the same manufacturer.
>>>>
>>>> If you buy a sample, I'll gladly help you figure out if it's any good
>>>> before
>>>> you buy a lot of them, in return for more data for my survey page ;-).
>>>>
>>>>        Arnd
>>>>
>>>
>>>
>>>
>>> --
>>> Christoph Derndorfer
>>> co-editor, olpcnews
>>> url: www.olpcnews.com
>>> e-mail: christoph at olpcnews.com
>>>
>>> _______________________________________________
>>> Devel mailing list
>>> Devel at lists.laptop.org
>>> http://lists.laptop.org/listinfo/devel
>>>
>>>
>>
>>
>> --
>> *Rodolfo D. Arce S.*
>> web: rodolfoarce.com
>> twitter: @rodolfoarces <http://twitter.com/rodolfoarces>
>>
>>
>>
>>
>
>
> --
> Christoph Derndorfer
> co-editor, olpcnews
> url: www.olpcnews.com
> e-mail: christoph at olpcnews.com
>

-- 
*Rodolfo D. Arce S.*
web: rodolfoarce.com
twitter: @rodolfoarces <http://twitter.com/rodolfoarces>
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