SD card format

Mac Air Mojave/Firefox

I put an SD card in for erase and format using Disk Utility. I did the 2 times erase.It formatted to Mac OS Ext. I could have picked Fat but it didnt say 32 so I went with the default. I put Ubuntu iso on it with Echer. Wow...its fast compared to my old PC using USB boot Creator.And the SD
works perfect as a boot for Ubuntu. I cant even tell the difference from a hard drive install. There is no discernible delay when using Ubuntu.
I think I will just leave the SD in permanently. But a couple things...When I boot into the boot screen it shows 3 drives,
the SSD,the SD card and another SD card icon that has only 1.9 gig on it. What is that? Should I erase and reformat to get rid of this?
The SD card is a PNY high speed 32 gig and its Really fast in this rig. I also got the message that said" this drive is not recognized etc"
and I selected ignore.

Your drive has a recovery partition that is about 1.9GB, the SSD is your Mac drive and the SD card is the SD card. DO NOT ERASE IT!

i erased the SD card and reformatted to FAT. If that notice pops up that says "doesnt recognize this drive etc" the one with "ignore"..how do you get it to stop displaying it.

For any drive larger than 8GB, you should be using FAT32 (or more appropriately ExFAT) as the format. FAT is VERY limited. I have no idea where you are getting that popup.