I wanted to use the USB port on my 2011 RS for playing MP3's, so I put some MP3's on an old 16GB flash drive and plugged it in and it worked, so I bought a 64GB flash drive and it would not work. I checked the owner's manual and GM web site for specifics on what drive formats and sizes will work, but found nothing useful for this vehicle. All I found was, "not all flash drives are compatible" and "only the 1st 10,000 songs will be recognized." I find this quite frustrating as you know someone at GM knows the exact specs, so why won't they publish them? I also found numerous posts from other users with questions, suggestions, and statements like, "mine just worked" which were not helpful at all. Being a computer geek, I performed a series of tests and the results follow. I hope this will be useful for someone else.
64GB, formatted with factory FAT32, does not work
64GB, formatted with NTFS, does not work
64GB, formatted with ExFAT, does not work
[ thinking the limit was less than 64GB, I tried incrementing ]
30GB partition on the 64GB drive, formatted FAT32, 32KB/cluster, works
32GB partition on the 64GB drive, formatted FAT32, 32KB/cluster, works
40GB partition on the 64GB drive, formatted FAT32, 32KB/cluster, works
48GB partition on the 64GB drive, formatted FAT32, 32KB/cluster, works
50GB partition on the 64GB drive, formatted FAT32, 32KB/cluster, works
55GB partition on the 64GB drive, formatted FAT32, 32KB/cluster, works
64GB partition (full drive), formatted FAT32, 32KB cluster size, works!
So it appears that the factory FAT32 format, with a cluster size that I did not make note of before reformatting, is incompatible, but reformatting with 32Kbytes per cluster works just fine.
Notes on Windows 7:
Windows 7 will only allow you to format drives larger than 32GB with NTFS,
so you need a 3rd party app to format them FAT32. I used fat32format, available here:
Also, if you go into the disk manager on windows 7, you will see that the option to delete the partition is greyed out. To delete it, you need to use DISKPART from the command line that comes with Windows 7, but I am not going to post instructions on how to do so, because this is a tool for advanced users and you can easily wipe out your hard drive if you don't know what you are doing. Advanced users can seek info on diskpart and figure it out pretty quickly. If you want to use the full drive you do not need this. You can take a drive with an NTFS format, run the fat32format program above, and reformat it to FAT32 without deleting the partition or volume.
Notes on brands:
Several people post things like "brand X works" or "brand Y does not work." Brand has NOTHING to do with it. As long as the device is USB 2.0 compliant, the radio has no idea what brand you are using. It just sees a USB flash drive.
Let me know if you find this posting useful.