I'm attempting to enable a transparent proxy on my RB493G on Mikrotik 6.27 software.

The Routerboard 493G sees the MicroSD.

I can format it ext3 just fine.

Where I get stuck from the instructions I find, is I can't find the 'store' menu, and if I skip this step my proxy doesn't seem to be able to use the micro-sd as it says it is 'full' even though it shows as >20GB of Free space.

If I create the proxy and tell it to cache to disk, the only disk options I get are 'pub' and the name of the volume or name of the volume/lost+found (ext3 format)

I also tried formatting it to FAT32. each time it got to about 74% and then just stopped progressing. I wandered off and played a couple rounds of Battlefield and it still hasn't progressed. i've let it sit in case it's some kind of issue.

What's the right way to set up the proxy on a disk? Without the store option all the 'how to's' i've seen don't work.

Did you try making folder on you SD Card so that you can mark your folder on SD card as folder for caching on disk?