Back.
I've sourced myself a 32GB SD card, and a WD My Passport 320GB USB disk. I hooked both up, the disk on the back USB port (I use the one on the side for my backup stick).
I have no issue whatsoever timeshifting to the USB disk, starts fine, I can navigate, and I can zap with hardly any noticable delay.
The SD card however is s different story, quite quickly it starts to generate I/O errors, after which it remounts R/O. A full check of the card in my laptop reveals no issues, no bad blocks, no write issues. So there seems to be something going on here.
The question is whether it is hardware related, as a test I used the same SD card in a uClan 4K Pro (equal to the first generation SF8008), and there it shows similar behaviour...