I had nothing but problems with a SanDisk 32GB Class 4 card, in my regular ol' RAZR. (See my other post in the RAZR Support forum.) Maybe the newer HD versions are a little different in some way.
Returned it and got a Microcenter branded 32GB card, Class 10. It was long-formatted in Win7 with FAT32 and 16kb allocation chunk. Then erased/formatted in the device. So far, it has worked fine.
It took quite a while for all the pics/vids to show up in My Gallery (about 3.6GB worth), I assume to make all the thumbnail files. It certainly would drain a lot of battery for the first day or 2 after I loaded all the data, and the stock ICS battery page would show Android OS using 50%+ on the usage even with the phone sitting idle doing nothing else...... had never seen that before (normally the screen uses the most).
Anyways, I now have about 15GB of music on the new Microcenter card, and I did the "Shuffle All" thing yesterday while working outside for a few hours. It worked fine, but I'm going to keep an eye on it regardless due to all the comments about the Class 10 cards. If anything goes awry, I'll certainly post back.
I'm going to let this thing run until probably past the holidays, and then burn on 215 and see if I can increase battery life. Maybe even go nuts and root it. Or better yet find a way to upgrade to a Maxx HD without breaking the bank.
