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Re: Android 6 and SD cards

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On 22/12/2016 20:58, Daniel James wrote:
> Having got my hands on a phone that runs Android 6 "Marshmallow" (a Moto G4
> Play) I thought I'd play around and try to answer a question I've asked
> several times that nobody has been able to answer.
>
> Background
>
> Android 6 can view an SD in either of two ways. It can be "portable storage"
> or "internal storage".
>
> If a card is used as portable storage Android uses it in pretty-much the
> same way as it has in earlier versions: it's used to store data in an
> ordinary filesystem in such a way that the card can be removed from the
> phone and used in another device (such as a PC).
>
> If a card is used as internal storage it becomes an extension of the phone's
> internal flash storage, and data that are stored on it can only be accessed
> in the Android device that formatted the card. Formatting the card this way
> enables it to be used to store apps (which in Android 6 you can't store in
> portable storage) and configuration data. etc.
>
> The thing that I hadn't been able to find out is: Can you partition the card
> so that it has one partition that can be used as internal storage and
> another partition that is portable and can be read on another device.
>
> Findings
>
> My initial findings are this isn't easy to do, if indeed you can do it at
> all.
>
> An SD card formatted as "portable storage" has a normal BIOS-style partition
> table, with a single Windows-style FAT32 or exFAT partition for the data.
>
> What I've discovered about an SD card that is formatted as "internal
> storage" is that it has a GPT partition table and two partitions as follows:
>
> One named android_meta with type:
> 19A710A2-B3CA-11E4-B026-10604B889DCF9BECF4E3-44ED-48AC-A831-50D3C0FD0539
>
> and one named android_expand with type:
> 193D1EA4-B3CA-11E4-B075-10604B889DCF 359AB3A6-F7B7-B687-0FC8-DB399A9BC232
>
> I didn't try to find out what sort of filesystem these partitions hold, and
> I believe that in any case at least one of them is encrypted.
>
> Conclusion
>
> My hope was that it would be possible to create an SD card with two
> partitions, one of which was an unencrypted FAT32 or exFAT partition for use
> as portable storage, and one of which was whatever was needed for internal
> storage, but what I've discovered is that Android doesn't even use the same
> partitioning system for these two types of card, so it seems pretty unlikely
> that we can have the best of both worlds.
>
> There are good security reasons for preventing the reading and writing of
> data from/to the internal storage of the Android device when the card is
> inserted into another device, but it's a pity that Google haven't made it
> possible to use just part of the SD card for internal storage and the rest
> for portable storage. It's particularly lamentable on the G4 Play (I don't
> know about other Marshmallow devices) because the rather simple camera app
> doesn't provide any means to select the destination for photographs, so they
> all go into internal memory rather than onto the SD card if it is set up as
> portable storage. JUST what you probably don't want!
>
> I hope this is of interest to someone.
>

Interesting!

I imagine that when you tell it to use the card as an extension of 
internal storage, it grabs the whole card and re-formats it with its 
proprietary format - so even if you did manage to create two partitions, 
they would be over-written.

There are pros and cons for both ways of using the card. A lot depends 
on how much internal storage the phone has to start with. My Moto G2 has 
only 8GB - which limits the number of apps you can install unless you 
format the SD card as internal. The downside is that if the card goes 
bad - and that's happened to two of mine - you stand to lose more than a 
bit of easily backed-up data, 'cos a lot of apps will disappear too and 
will need to be re-installed on a new card.

If my phone had 16GB of internal storage I would probably use the card 
as 'portable'. Even if the camera insisted on putting photos in internal 
storage, it shouldn't be too difficult to move them onto the card.
-- 
Cheers,
Roger
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Android 6 and SD cards Daniel James <daniel@me.invalid> - 2016-12-22 20:58 +0000
  Re: Android 6 and SD cards Roger Mills <watt.tyler@gmail.com> - 2016-12-22 21:34 +0000
  Re: Android 6 and SD cards Daniel James <daniel@me.invalid> - 2016-12-22 21:39 +0000
    Re: Android 6 and SD cards The Real Bev <bashley101@gmail.com> - 2016-12-22 21:45 -0800
      Re: Android 6 and SD cards tlvp <mPiOsUcB.EtLlLvEp@att.net> - 2016-12-23 12:09 -0500
        Re: Android 6 and SD cards tlvp <mPiOsUcB.EtLlLvEp@att.net> - 2016-12-24 11:51 -0500
          Re: Android 6 and SD cards The Real Bev <bashley101@gmail.com> - 2016-12-24 10:06 -0800
            Re: Android 6 and SD cards tlvp <mPiOsUcB.EtLlLvEp@att.net> - 2016-12-24 13:21 -0500
              Re: Android 6 and SD cards The Real Bev <bashley101@gmail.com> - 2016-12-24 11:54 -0800
                Re: Android 6 and SD cards tlvp <mPiOsUcB.EtLlLvEp@att.net> - 2016-12-25 00:01 -0500
                Re: Android 6 and SD cards The Real Bev <bashley101@gmail.com> - 2016-12-24 21:44 -0800
                Re: Android 6 and SD cards tlvp <mPiOsUcB.EtLlLvEp@att.net> - 2016-12-25 14:18 -0500
                Re: Android 6 and SD cards ANTant@zimage.com (Ant) - 2016-12-26 06:45 -0600
                Re: Android 6 and SD cards The Real Bev <bashley101@gmail.com> - 2016-12-26 08:22 -0800
                Re: Android 6 and SD cards ANTant@zimage.com (Ant) - 2016-12-27 03:58 -0600
                Re: Android 6 and SD cards Frank Slootweg <this@ddress.is.invalid> - 2016-12-26 18:50 +0000
      Re: Android 6 and SD cards Daniel James <daniel@me.invalid> - 2016-12-27 15:31 +0000
        Re: Android 6 and SD cards The Real Bev <bashley101@gmail.com> - 2016-12-27 09:04 -0800
          Re: Android 6 and SD cards "Carlos E. R." <robin_listas@invalid.es> - 2016-12-28 20:52 +0100
        Re: Android 6 and SD cards tlvp <mPiOsUcB.EtLlLvEp@att.net> - 2016-12-27 23:46 -0500
          Re: Android 6 and SD cards Daniel James <daniel@me.invalid> - 2016-12-28 10:51 +0000
  Re: Android 6 and SD cards tlvp <mPiOsUcB.EtLlLvEp@att.net> - 2016-12-22 20:14 -0500
  Re: Android 6 and SD cards The Real Bev <bashley101@gmail.com> - 2016-12-22 21:43 -0800
    Re: Android 6 and SD cards Daniel James <daniel@me.invalid> - 2016-12-27 15:31 +0000
      Re: Android 6 and SD cards The Real Bev <bashley101@gmail.com> - 2016-12-27 08:59 -0800
        Re: Android 6 and SD cards Daniel James <daniel@me.invalid> - 2016-12-28 10:51 +0000
          Re: Android 6 and SD cards AL <l452236747@invalid.com> - 2016-12-28 09:10 -0700
          Re: Android 6 and SD cards AL <l452236747@invalid.com> - 2016-12-29 07:47 -0700
            Re: Android 6 and SD cards nospam <nospam@nospam.invalid> - 2016-12-29 16:19 -0500
            Re: Android 6 and SD cards tlvp <mPiOsUcB.EtLlLvEp@att.net> - 2016-12-29 15:13 -0500
          Re: Android 6 and SD cards The Real Bev <bashley101@gmail.com> - 2016-12-28 11:20 -0800
            Re: Android 6 and SD cards The Real Bev <bashley101@gmail.com> - 2016-12-28 15:25 -0800
          Re: Android 6 and SD cards tlvp <mPiOsUcB.EtLlLvEp@att.net> - 2016-12-29 04:04 -0500
            Re: Android 6 and SD cards nospam <nospam@nospam.invalid> - 2016-12-29 12:02 -0500
            Re: Android 6 and SD cards tlvp <mPiOsUcB.EtLlLvEp@att.net> - 2016-12-29 15:06 -0500
          Re: Android 6 and SD cards "Carlos E. R." <robin_listas@invalid.es> - 2016-12-28 21:15 +0100
      Re: Android 6 and SD cards Piet <www.godfatherof.nl/@opt-in.invalid> - 2016-12-27 18:55 +0100
        Re: Android 6 and SD cards Daniel James <daniel@me.invalid> - 2016-12-28 10:51 +0000
      Re: Android 6 and SD cards "Carlos E. R." <robin_listas@invalid.es> - 2016-12-28 21:06 +0100

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