I figured out how to easily do this without windows

• installed exfat-utils to my Easy Debian sandbox
• formatted a partition to exfat and verified it's mountable
• booted to ubiboot console and mounted it as exfat

-> everything works OK for me.

So, Tmavica, there must be some glitch in the ubiboot-02_230913 alpha that causes this to not behave correctly for you.

Can you try the following:

• go to ubiboot maintanance console
• unmount all exported filesystems (if any) from your PC (this is important or the next command does not work)
• remove the exports on N9 by command "echo "" > /sys/devices/platform/musb_hdrc/gadget/lun0/file"
• check that there are no mounts of mmcblk0 by command "mount"
• try to mount the partition with command "mount -t exfat /dev/mmcblk0p1 /mnt/1" (assuming that it is your partition 1 that is exfat)
• check with command "mount" that the partition is mounted correctly

and you should see something like this:

/ #
/ # mount -t exfat /dev/mmcblk0p1 /mnt/1
/ # mount
rootfs on / type rootfs (rw)
none on /dev type devtmpfs (rw,relatime,size=498796k,nr_inodes=124699,mode=75 5)
proc on /proc type proc (rw,relatime)
sysfs on /sys type sysfs (rw,relatime)
none on /tmp type tmpfs (rw,relatime,size=10240k)
/proc/sys/debug on /proc/sys/debug type debugfs (rw,relatime)
none on /var/run type tmpfs (rw,nosuid,noatime,size=256k,mode=755)
devpts on /dev/pts type devpts (rw,relatime,mode=600)
/dev/mmcblk0p1 on /mnt/1 type exfat (rw,relatime,fmask=0022,dmask=0022,iocharset=utf8, namecase=0,errors=remount-ro)
/ #