How is the drive formatted?

I have an ipod classic "7.5 gen" converted to use a 256gb sdxc card. It also uses emcore/rockbox.

I am in search of a means to load up the card external to the ipod, as rockbox usb is very slow (I mean, its do-able, but it can take all night and half the following day to fully load it from blank).

With a 5gen ipod once rockboxed the drive can be loaded up external to the ipod by connecting it directly to the PC (which is maybe 5 times as fast, maybe more) but the 6gen and above obfuscates the drive format/partition structure, preventing you from doing that. The PC can't read or write to the partitions or even understand them.

I'm sure that _somewhere_ out there there must be some information as to exactly what it is the 6-7.5gen ipod classics do that makes the drive not readable when connected to the PC. Surely someone must know?