[Galaxy S III Q&A, Help & Troubleshooting] iamthemandroid:
I bought this 64GB SanDisk sd card (http://www.amazon.com/SanDisk-microSDXC-Memory-Adapter-SDSDQUA-064G-U46A/dp/B007WTAJTO) which was working fine in my stock ROM for a few weeks. I then flashed a custom ROM (latest stable Resurrection Remix) that didn't recognize it. When I immediately flashed back to the stock ROM it also didn't recognize the card anymore. Surely that's not an issue of physical damage, as the timing would be quite coincidental! Something happened while installing that custom ROM to change maybe partition tables or whatever on that sd card.

What tells me for sure that the card is NOT physically damaged is that I can successfully store nandroid backups to it and restore from nandroid backups on it, but only from ClockworkMod Recovery 5.5.*. I've tried many other recoveries (even the newer, touch-based ClockwordMod Recoveries), as well as a couple more ROMs and nothing else recognizes the drive at all. But clearly the drive itself isn't damaged. Unfortunately ClockworkMod Recovery 5.5.* doesn't have any sort of ability to let me connect to my computer in USB mass storage mode or otherwise get the data off of the card :(

I was able to restore data from the a disk dump of the card using 'photorec' recovery but it restored every one of the 90,000 files on that card (even though only about 1,000 are the ones I actually need and not 'system' or 'backup' files) into a restore directory where every file name is named like f3728467371291.gz and with all the same timestamps, so it would take me forever to figure out which files are mine, so mounting the drive would really help.

I also realize using this card with my Android may have been risky in the first place, see http://www.transformerforums.com/forum/general-discussion/28678-sandisk-64gb-microsd-woes.html, but it was working successfully and the card itself isn't damaged so there must be a way to get the data off in a sane way. (I won't use this card in future with my Android.)

I put the sd card into my Ubuntu 12.04 laptop and it didn't get recognized automatically like what happens with other sd cards. So I dig some digging and it says that the card (at /dev/mmcblk0, with partition /dev/mmcblk0p1) is 'HPFS/NTFS/exFAT' in the output below (but first I took a 'dd' disk images of both the whole card, mmcblk0, and the partition, mmcblk0p1).

Any help you could provide would be greatly appreciated. Thanks!

$ sudo dd if=/dev/mmcblk0 of=~/mmcblk0
$ sudo dd if=/dev/mmcblk0p1 of=~/mmcblk0p1

$ sudo fdisk -l ~/mmcblk0

Disk mmcblk0: 63.9 GB, 63864569856 bytes
255 heads, 63 sectors/track, 7764 cylinders, total 124735488 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00000000

Device Boot Start End Blocks Id System
mmcblk0p1 32768 124735487 62351360 7 HPFS/NTFS/exFAT

Trying to mount as NTFS but get error:

$ sudo mount -t ntfs ~/mmcblk0p1 /mnt/sdcard
NTFS signature is missing.
Failed to mount '/dev/mmcblk0p1': Invalid argument
The device '/dev/mmcblk0p1' doesn't seem to have a valid NTFS.
Maybe the wrong device is used? Or the whole disk instead of a
partition (e.g. /dev/sda, not /dev/sda1)? Or the other way around?

Trying to mount as exFAT but get error:

$ sudo apt-add-repository ppa:relan/exfat
$ sudo apt-get update
$ sudo apt-get install fuse-exfat

$ sudo mount -t exfat ~/mmcblk0p1 /mnt/sdcard
FUSE exfat 0.9.8
ERROR: exFAT file system is not found.

Getting some info about the whole card:

$ sudo file -s ~/mmcblk0
/dev/mmcblk0: x86 boot sector; partition 1: ID=0x7, starthead 10, startsector 32768, 124702720 sectors, extended partition table (last)\011, code offset 0x0

Getting some info about the partition:

$ sudo file -s ~/mmcblk0p1
/dev/mmcblk0p1: x86 boot sector, code offset 0x52

Do you have any idea how I could mount this card successfully?