I just got a 32GB SDcard for my MarkV too, and it would not recognize the card. I played with several different options until I found the right solution. The answer was to format the SD card as an ext2 filesystem.
To make this work, I had to SSH into the MarkV ... login as root, and run:
# mkfs.ext2 /dev/sdcard/sd1
When you look at the fstab it shows that the device node /dev/sdcard/sd1 is supposed to mount on the mountpoint /sd. However, there were already files in /sd and mounting the SD card there would effectively make those files inaccessible. So I first copied those files to the SD card after formatting it ... THEN mounted it.
For 32GB, this took a while, but when completed, I created a new directory (so as not to overwrite the existing directory, /sd) and then mounted the card:
# mkdir /sd1
# mount -w /dev/sdcard/sd1 /sd1
Then I copied the files from /sd (which was part of the root filesystem) over to the SDcard (so I could then mount the sdcard where it belongs)
# cp -a /sd/* /sd1
Next unmount the SD card and remount it where it belongs:
# umount /sd1
# mount -w /dev/sdcard/sd1 /sd
Finally ... clean up the extra directory that was created for copying:
# rmdir /sd1
Now I am able to see the full space available under the Status window, and am able to download large infusions to the 32Gb SD card.
Hopefully that helps some of you who may have seen the same problem.
