[General Questions and Answers] vantt1:
Hello,

TL;DR: I know how to format memory cards. The problem is; how do I get the Galaxy S2 to properly mount and access a 64 GB FAT32 MicroSD?

Long story:

I recently bought two

brand new

SanDisk 64 GB Mobile Ultra SDXC UHS-I Class 10 MicroSD cards (not on the internet, but from a reputable electronics retailer), in hopes of expanding the memory of my Samsung Galaxy S2 and Asus Slider SL101. I know that the Galaxy S2 does not officially support 64GB MicroSD cards, but after reading a few posts about successfully getting them to work after formatting them to FAT32, I gave it a shot.

Initially, both cards appeared to work fine. I plugged them both into my PC, and both cards mounted fine and appeared in the Explorer window as expected. And given that these particular 64 GB cards are designed specifically for use with an Android Smartphone, I put one of them (let's call this Card A - Card B hasn't been touched yet) into my Galaxy S2.

(Note: My Galaxy S2 was running Resurrection Remix 3.1.2 when I did this)

The phone booted up as usual, and I saw the "Preparing SD Card..." text up in the status bar appear, but then it disappeared quicker than it should have. I opened up 6 file managers (ASTRO, OI, CM, Root Explorer, AndroZip and ES File Explorer) and tried to access the extSD directory, but it always shows up as empty; not even a LOST.DIR existed. Nothing could be copied to the extSD directory.

Then I plugged Card A into my PC, and checked the filesystem. It turns out that the card is formatted to exFAT by default. This isn't what I expected, because:

1. exFAT is a licensed proprietary filesystem, not supported by Android due to licensing

2. Only Samsung's newer devices (i.e. Galaxy S3, Note 2, Note 10.1) have partial unofficial exFAT support hacked into their stock TouchWiz ROM

3. Samsung's newer TouchWiz devices do not constitute for all "Android Smartphones", as SanDisk should know

So then I tried to copy a few videos to Card A. But only one video could be copied, then the card would unmount itself. Physically reconnecting it mounts it again, and performing no operations to it will leave it mounted. But as soon as I try to copy again or run a CHKDSK, it would unmount.

I opened up EASEUS Partition Manager and saw that Card A had two partitions - a large ~59.46 GB partition, and the dreaded unallocated 16 MB known to plague SanDisk's 64 GB MicroSDs. I formatted the large partition to FAT32 with a 8192kb cluster size, and the same aforementioned problem still occurs. I sent this card back for replacement, and am still awaiting news on it.

Card B is quite interesting. I plugged it into my computer, everything seems fine, so then I try it on my Asus Slider. Surprisingly, because it is an exFAT volume, the Slider detects it perfectly fine - correct capacity, LOST.DIR exists and I can perform file operations on it. I copied 30 GB of files onto it with no problems. The problems arise when I format it to FAT32.

(Note: My Asus Slider is running stock rooted 4.0.3 and it can natively read FAT32, exFAT and even NTFS. The single USB port it has can also operate a 2.5" NTFS external hard drive running off USB power.)

Card B also has the mysterious 16 MB unallocated space. This time, I deleted the exFAT partition (instead of directly formatting it to FAT32) creating one large unallocated space, THEN I formatted it to FAT32. I copied the same files to it, and it didn't unmount like Card A did.

(Note: My Galaxy S2 is now running Vanilla RootBox v3.8)

I try to use Card B in my Galaxy S2, and it hangs on the RootBox boot animation. My Slider shows "Preparing External Storage..."

, then quickly disappears, much like Card A did on RR 3.1.2 as previously mentioned. It boots again if I use my 32 GB SDHD MicroSD.

Card B still reads fine as a FAT32 volume on my PC. No sudden unmounts or anything.

And all that brings me here, seeking help from the almighty XDA Forums. Does anyone have any idea why this is happening? How can I get it to work on my Galaxy S2?

UPDATE: My replacement card seems to work without problems. Statistical chance of card failure is now 66.67% instead of 100%.

2nd UPDATE: My second replacement also seems to work without problems. Statistical chance of card failure is now 50%.