Why is the SD-card mounted to “/sdcard/external_sd” instead of “/sdcard” (or “/mnt/sdcard”)?

Question

I recently upgraded my phone to an LG Motion 4G (Android 4 ICS). I see that the sdcard is mounted at /sdcard/external_sd. I also noticed that this appears to be the same with some other newer models. Apps expect the sdcard to be at /sdcard. I assume the manufacturers want to include a lot of internal storage, but why mount internal storage at /sdcard? Shouldn't this be against some form of Android specification standard?

Answer 1

The reason is the history of Android: The first generation of Android devices only hand a small amount of internal storage (around 100-400MiB) that was mounted under /data.

Next devices with a, at that time external, SD-card came out. The SD card was mounted under /mnt/sdcard.

After that, devices with large internal storage came on the market. This storage was portioned, because /mnt/sdcard had become the default place for big data chunks from apps, pictures and such. So the Android environment had to have a /data and /mnt/sdcard directory. Therefore one parition was for /data, the other for /mnt/sdcard. This is the reason why you storage space could become low (the /data partition) even if there is plenty of space on /mnt/sdcard.

This situation was improved with Android 3.0: /data and /mnt/sdcard are now pointing to the same parition. ^{Good job Google, that could have been done versions ago.} Which is also the reason why app2sd is no more needed on Andriod 3.0 or higher: You would only move the data within the same volume.

Now we come to the answer if your question: Since /mnt/sdcard is already mounted on the internal storage, an external SD-card has to use a different mount point. And this mount point is not specified by Google. It could be

• /mnt/sdcard/ext_sd
• /mnt/external
• /mnt/extSdCard
• /mnt/sdcard/external_sd
• etc.

The API call getExternalStorageDirectory() usually points to the internal storage direcotry. This behavior is documented. There are open source projects that provide tools to find the external SD-card directory in a canonical way.

Answer 2

Forcing external SD mount away from /mnt/sdcard has no technical merit, it is Google's way of helping hardware vendors to create a differentiation point for phones with more internal memory.

There is no reason why applications have to find a way to locate the external card when /mnt/sdcard was clearly the place the sdcard should have been and Google's undefined way of loading external SD card is another less than consumer friendly plot to make external SD card less useful in newer Android devices. There is NO reason why /data and /mnt/sdcard had to be merged into the same partition on newer version of Android except for manufacturer to differentiate phones with larger internal memory from lower cost units with less internal memory. Even if the merge had to be done, Google could have clearly defined a STANDARD new mounting point for the external SD cards instead of leaving it completely vague. This is completely working against preventing further "segmentation" of the Android eco-system by a clumsy design to help vendor differentiation of higher end phones against lower cost units with less built-in memory.

Android app binaries are tiny, phones with 1-2 Gigs of internal memory should have way more than enough space for hundreds of apps, and all the large data could be safely tucked way on an external SD card. But then vendors realized they had to have a way to differentiate their higher end product, and claiming a higher internal memory become part of that scheme and crippling the usefulness of external memory is the other integrated part this scheme required for this to work fully hence the less helpful API to find external sd cards and the unstandardized mounting points.

So: No, mounting SD card at a place other than /mnt/sdcard is nothing but a business strategy for selling higher priced new phones under newer version of Android, nothing more than that. Just imagine, if the Nexus 4 8GB and Nexus 16GB can both use 64GB of external sd card for application and media, is there a reason for anyone to buy the 16 GB version? That extra 8 GB of NAND memory is not surely not worth $50 price difference if external SD cards are involved. Since most components in a smart phone pretty much has to be the same (RAM, processor, radios), the only area left for more profit margin is the internal memory space, and hence the weird external memry mounting point.

Also has everyone also noticed the absence of external SD support from current crop of "Google" branded android devices? This trend will keep expanding in "top tier" Android devices. External SD card support was a key differentiation for Android devices to overtake iPhone's dominance in mobile market. Now with Android ruling supreme in the numbers game, there's little need for this profit sapping practice to be up kept for much longer.

I won't be surprised by Android 5.0, the external SD card support would be a thing of the past. Because if it's hard to apps to find externals SD card, then most program will just simply use the known /data and /mnt/sdcard locations, with most apps use more and more stored data for its operation, a vibrant product mark up strategy is created out of "thin air" simply by not mount external SD card at /mnt/sdcard.