2 SD card slots and rootfs on internal SD card - maybe VFAT + fs images?

Andy Green andy at openmoko.com
Sat Apr 12 11:10:57 CEST 2008

Hash: SHA1

Somebody in the thread at some point said:

|> I think two cards is not needed, you just put your big card in the
|> device when you buy a new card, copying over the handful of "system
|> files" from the original card on a PC on easy VFAT.
|> I suspect wanting a second removable card is just a crutch because we
|> did a rubbish job making the one internal card a) big enough and b)
|> easily accessible over network at high bandwidth.  If it is true we need
|> to attack the true issue.

| the reason i am mumbling 2 cards is this:
| 1. internal card is safe - can't be removed without a system
powerdown. we can
| rely on it.

You can keep power up on USB and pull the battery OK, but point taken.

| 2. external card is removable any time - like any removable storage u
have with
| sd-card etc. readers on laptops/desktops/anywhere else. this is where your
| "media" goes - music, photos, movies etc. etc. - stuff you like to
| around and plug in/out of multiple devices and that you may want many
gb of
| storage for. buy a few 8gb micro-sd cards and you can traipse around a
lot of
| music/videos etc. etc.

Yes Daniel explained the same things, but when I looked closely at it, I
didn't really believe it or see it happening.  There are so many
different physical formats for flash it is super unlikely you have
another device with microSD, I don't.  I have Sony Memory Stick, USB
thumb drives, CF cards, I even have some big oldstyle SD.  I have
nothing to share that card with.  Daniel mentioned camera pic transfer,
that can be done in a flash-format-agnostic way using USB host to the
camera without card ejection.

When I looked at "lot of music and videos" also it seemed to me putting
a single 8GB or 16GB card inside the device will be fine for normal
case.  That is a buttload of storage, it is a lot of long transcoded
video as well... and with video, once you saw it, typically you do not
need it to see again for a long time.  So for video there is often high
turnover for the storage space naturally.

The real question is what leads people to see themselves ejecting that
SD card?  The answer is because we didn't provide an alternative fantasy
for them where they see themselves easily and smoothly connecting to the
SD card storage remotely without touching the device and managing the
storage space reliably and at high bandwidths from a PC or whatever.

In .tw we touched on this and again you had done thinking on it already,
I siad that Samba would suck badly and always caused me trouble and to
expose the SD card as USB mass storage device.  But you pointed out that
this is a block-level thing that would conflict with any mount in the
device.  So we need another story for this I think that truly scratches
the same itch that makes people want to physically eject cards.

| 3. external card is ok if a user removes it any time during operation - it
| won't screw up the core fs's we rely on (/home for user dir and
config, and /
| for base os).

What's the motive for removing it though... all we really have is
because the user carries around many 8GB microSD cards with media on
them, I do not think that is going to be a common scenario on cost
grounds alone.  OTOH replacing the shipped SD card with a single huge
hulking one I can see happen quite a bit.

| 4. an EASILY accessible external card is good for usability and users.
it makes
| industrial design less slick though as space for the slot has to be
| for.

Again this presupposes there is a good valid motive for removing the
card during normal usage.

- -Andy
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