Mailing List Archive

jffs2 on mmc?
I've been looking into booting from the sdcard and was wondering why
none of the "how to's" suggest formatting the card with jffs2. There's
lots of debate between using ext2 or ext3, but nothing on using jffs2.
Is there a simple reason for this I'm missing?
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Re: jffs2 on mmc? [ In reply to ]
JFFS2 is designed to be used on a raw flash device. SD cards have a
controller inside that hides the access to the raw flash and deals with
things like write levelling, that JFFS2 would otherwise have to do in
software.

Ed Okerson

> I've been looking into booting from the sdcard and was wondering why
> none of the "how to's" suggest formatting the card with jffs2. There's
> lots of debate between using ext2 or ext3, but nothing on using jffs2.
> Is there a simple reason for this I'm missing?
> _______________________________________________
> maemo-developers mailing list
> maemo-developers@maemo.org
> https://lists.maemo.org/mailman/listinfo/maemo-developers
>


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Re: jffs2 on mmc? [ In reply to ]
ed@okerson.com wrote:

>> I've been looking into booting from the sdcard and was wondering why
>> none of the "how to's" suggest formatting the card with jffs2.
>> There's
>> lots of debate between using ext2 or ext3, but nothing on using
>> jffs2.
>> Is there a simple reason for this I'm missing?
>
> JFFS2 is designed to be used on a raw flash device. SD cards have a
> controller inside that hides the access to the raw flash and deals
> with
> things like write levelling, that JFFS2 would otherwise have to do in
> software.

Yes, as Ed says, jffs2 would serve no purpose for an SD card. Besides,
can you imagine how long it would take to process a 16GB card into
memory every mount? :shudder:
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Re: jffs2 on mmc? [ In reply to ]
I heard that the jffs2 had support for sdcards (I'm assuming that
means it doesn't do wear-leveling and leaves it to the
microcontroller), but that it still checks every bit on the card
before loading the OS. However, I like the idea that JFFS2 has
journaling which ext2 does not and probably does it in a way that's
not requiring too many extra writes (like ext3). Maybe I'll try it
with a reasonably sized partition and hope it doesn't take too long to
boot.

On Sun, May 18, 2008 at 5:24 PM, Tim Tisdall <tisdall@gmail.com> wrote:
> I heard that the jffs2 had support for sdcards (I'm assuming that
> means it doesn't do wear-leveling and leaves it to the
> microcontroller), but that it still checks every bit on the card
> before loading the OS. However, I like the idea that JFFS2 has
> journaling which ext2 does not and probably does it in a way that's
> not requiring too many extra writes (like ext3). Maybe I'll try it
> with a reasonably sized partition and hope it doesn't take too long to
> boot.
>
> On Sun, May 18, 2008 at 1:52 AM, Ryan Abel <rabelg5@gmail.com> wrote:
>> ed@okerson.com wrote:
>>
>>>> I've been looking into booting from the sdcard and was wondering why
>>>> none of the "how to's" suggest formatting the card with jffs2.
>>>> There's
>>>> lots of debate between using ext2 or ext3, but nothing on using
>>>> jffs2.
>>>> Is there a simple reason for this I'm missing?
>>>
>>> JFFS2 is designed to be used on a raw flash device. SD cards have a
>>> controller inside that hides the access to the raw flash and deals
>>> with
>>> things like write levelling, that JFFS2 would otherwise have to do in
>>> software.
>>
>> Yes, as Ed says, jffs2 would serve no purpose for an SD card. Besides,
>> can you imagine how long it would take to process a 16GB card into
>> memory every mount? :shudder:
>> _______________________________________________
>> maemo-developers mailing list
>> maemo-developers@maemo.org
>> https://lists.maemo.org/mailman/listinfo/maemo-developers
>>
>
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Re: jffs2 on mmc? [ In reply to ]
Personally I think it will be a lot easier to just try ext3 - what are
your concerns with extra writes?

Just because you might theoretically be able to use jffs2 on an SD card
doesn't make it easy. Try using mkfs.jffs2 on your desktop and see what
you get back.

Tim Tisdall wrote:
> I heard that the jffs2 had support for sdcards (I'm assuming that
> means it doesn't do wear-leveling and leaves it to the
> microcontroller), but that it still checks every bit on the card
> before loading the OS. However, I like the idea that JFFS2 has
> journaling which ext2 does not and probably does it in a way that's
> not requiring too many extra writes (like ext3). Maybe I'll try it
> with a reasonably sized partition and hope it doesn't take too long to
> boot.
>
> On Sun, May 18, 2008 at 5:24 PM, Tim Tisdall <tisdall@gmail.com> wrote:
>> I heard that the jffs2 had support for sdcards (I'm assuming that
>> means it doesn't do wear-leveling and leaves it to the
>> microcontroller), but that it still checks every bit on the card
>> before loading the OS. However, I like the idea that JFFS2 has
>> journaling which ext2 does not and probably does it in a way that's
>> not requiring too many extra writes (like ext3). Maybe I'll try it
>> with a reasonably sized partition and hope it doesn't take too long to
>> boot.
>>
>> On Sun, May 18, 2008 at 1:52 AM, Ryan Abel <rabelg5@gmail.com> wrote:
>>> ed@okerson.com wrote:
>>>
>>>>> I've been looking into booting from the sdcard and was wondering why
>>>>> none of the "how to's" suggest formatting the card with jffs2.
>>>>> There's
>>>>> lots of debate between using ext2 or ext3, but nothing on using
>>>>> jffs2.
>>>>> Is there a simple reason for this I'm missing?
>>>> JFFS2 is designed to be used on a raw flash device. SD cards have a
>>>> controller inside that hides the access to the raw flash and deals
>>>> with
>>>> things like write levelling, that JFFS2 would otherwise have to do in
>>>> software.
>>> Yes, as Ed says, jffs2 would serve no purpose for an SD card. Besides,
>>> can you imagine how long it would take to process a 16GB card into
>>> memory every mount? :shudder:
>>> _______________________________________________
>>> maemo-developers mailing list
>>> maemo-developers@maemo.org
>>> https://lists.maemo.org/mailman/listinfo/maemo-developers
>>>
> _______________________________________________
> maemo-developers mailing list
> maemo-developers@maemo.org
> https://lists.maemo.org/mailman/listinfo/maemo-developers
>
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Re: jffs2 on mmc? [ In reply to ]
Hi,

ext Tim Tisdall wrote:
> I heard that the jffs2 had support for sdcards (I'm assuming that
> means it doesn't do wear-leveling and leaves it to the
> microcontroller), but that it still checks every bit on the card
> before loading the OS. However, I like the idea that JFFS2 has
> journaling which ext2 does not and probably does it in a way that's
> not requiring too many extra writes (like ext3). Maybe I'll try it
> with a reasonably sized partition and hope it doesn't take too long to
> boot.

JFFS2 is not really suitable for larger file systems.

If you'd use it on full 8GB memory card, it would probably eat
all memory than the device has (JFFS2 keeps whole disk structure
in memory, and the structures for open files take more RAM than
for non-open ones).


- Eero
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