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Are there any particular advantages/disadvantages to storing apps on the external storage of an Android device? As I have a Nexus S, I can't think of advantages for me as I can't remove the storage, also the internal storage is more than enough for my needs.

I noticed that on phone start up, when I had all my apps moved to USB storage it was quite sluggish to register all the apps on the menu/home screens.

I also read somewhere that having a wallpaper set from a photo that was stored on the external memory actually drained quite a bit of battery too with all the reads (although I think this may have been a bug).

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You haven't got an HTC phone, you don't have all their problems with tiny internal storage. There's no real reason for you to move any apps to SD. –  GAThrawn May 27 '11 at 15:49
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3 Answers

up vote 20 down vote accepted

Advantages:

  • Extend the available space on internal memory for installing more apps.
    Although some parts of the app still stay on the internal memory (data and settings,) it still frees up a significant amount of space. For older handsets with 150MB of free space (G1, MT3G, etc.) this is a huge improvement. For owners of these devices this advantage alone outweighs any disadvantages that this method brings.

Disadvantages:

  • Cannot use apps moved to SD Card if it's unmounted.
    Kind of self-explanatory: if you un-mount the SD Card for removal, the apps that reside on it need to be stopped and um-mounted as well to prevent crashes and data loss if you do remove the card.
  • Inability to use widgets or sync adapters when you move those apps to SD Card.
    This is a design limitation that stands from the above point. Since the apps stored on SD Cards need to be able to be removed on demand, things like widgets or apps that hook into your account settings (e.g. Skype, LinkedIn) will crash, with no easy way to re-start them. So Google made a compromise by requiring these apps to stay on internal memory. Even if you do manage to force them to the SD Card (some custom ROMs allow this), you simply won't be able to use them.
  • Longer boot-up and shut-down times when the system mounts/un-mounts all of the apps stored on SD Card.
    Apps that were moved to SD Card are not stored in plain sight to prevent rampant piracy. Instead, Android sets aside some space and creates a virtual partition for each app that you move. This means that at the initial boot-up, all these virtual partitions need to be mounted before apps stored on them can be accessed. The same holds true when you turn the handset off - each virtual partition is un-mounted before other shutdown processes can happen. Depending on the number of installed apps this can take an extra minute or even longer for the system to "stabilize" upon boot-up (and about 20 extra seconds for shutting down.) Once this happens though, launching these apps doesn't take any longer than those on internal memory.
  • Extra wear on the SD Card.
    This point is debatable, since writing to SD Card (which causes wear) doesn't happen that often. And besides, the SD Cards these days are cheap enough to not worry about their life time.
  • Apps require an update to support this functionality.
    Ability to be moved to SD Card is not automatically granted to older apps. Developers must change their apps to support this feature and issue an update via Market (or whatever distribution method they use.) Some older apps may not be supported any longer, and so may never get this feature. Although some custom ROMs can override this, for most people that are running stock firmware, this is a problem.

For newer devices with gigabytes of internal memory moving apps to external storage is not necessary, since space is not an issue. However for handsets with low memory it's an invaluable tool that extends their shelf life for their owners.

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Another drawback: when restoring from backups, all restored apps go into main memory - which causes the restore to fail when main memory fills up. –  David Apr 16 '12 at 21:07
    
@David That really depends on the application you are using for backup/restore purposes. Better ones (Titanium Backup for example) will give you an option for the restore location, and allow to restore either directly to SD Card, or to the original location. –  Chahk Apr 17 '12 at 0:14
    
sweet! Nice to know; thanks. –  David Apr 17 '12 at 15:31
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For some phones and devices (especially the older ones) the internal storage is quite limited. Every application (and it's data files) take precious space. I.e. my Ideos has 512MB and was nearly full before I started "evacuating" apps to the SD card.

Another factor is the ability to backup your apps and data, or move them to another device.

Other than that, you are right in your observation that apps load slower from the external storage compared to the internal storage. This is very visible if you have those apps' shortcuts on your home screen - you'll see a generic Android icon for the first 30 seconds until the app is located on the card.

I found that switching to a class 6 microSD (I had the default class 2 that came with the phone) improved the situation considerably. Still, it takes my phone about 20 seconds to "equalize" following a cold start.

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Ooh, default class 2? That's harsh. –  Matthew Read May 27 '11 at 17:01
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As far as I know there are limitation for the use of dashboard-widgets for applications on the SD card.

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