32GB memory card has only 256MB after formatting on a Mac mini

mccass wrote:

I think I solved it (with your help). If I select the OWC reader I see 31Mb (blue) and 31Gb (red). With the focus on the OWC reader I press "wis" (format?!) and the Card is 32 GB again. Thank you all for your help!!

https://discussions.apple.com/content/attachment/e25f6a5a-96c5-4acf-b238-1a68c0656228

Good work, you're welcome.

The command line output clearly shows the missing storage is in an unpartitioned area of the SD Card. Like I said, macOS & Disk Utility like to hide things from the user. Since Disk Utility GUI only shows the 268MB volume, that is all you will ever see unless you select the physical drive to erase. The Apple article @den.thed linked at the beginning of the thread shows each required step to erase the whole physical drive which from your screenshots of Disk Utility is the item named "OWC TB3 SD Card Reader Media".

mccass wrote:

I think I solved it (with your help). If I select the OWC reader I see 31Mb (blue) and 31Gb (red). With the focus on the OWC reader I press "wis" (format?!) and the Card is 32 GB again. Thank you all for your help!!

https://discussions.apple.com/content/attachment/e25f6a5a-96c5-4acf-b238-1a68c0656228

That only formatted the 32GB section, but likely left the second 268MB partition as well. Select the "OWC TB3 SD Card Reader Media" item on the left pane of Disk Utility and click Erase. You will then have a single 32GB partition on the SD Card.

Looks like that external card is split into different volumes and we are only seeing the information for one volume.

Click on the View box and select Show All Devices.

Select the external card in the Disk Utility sidebar and post another screenshot.

Disconnect all other external drives. With only this SD Card connected, run the following Terminal command which will show us the complete drive layout (Disk Utility hides a lot of details from view to "protect" the user & "simplify" things):

diskutil  list  external

If you are using this SD Card as a boot disk, then any boot images you put onto the card can make the card look different and will easily confuse macOS & Disk Utility. It is not unusual for macOS to have issues partitioning & formatting such a disk. I find that sometimes I must use the command line to write zeroes to the beginning of such a disk to destroy the existing partition table & layout before Disk Utility can properly erase the disk. Once in a while this must be done on a Windows or Linux system because macOS just cannot handle some situations.

Hmm... looks like something is wonky with the OWC card reader or the SD card.

Try ejecting and re-moving the SD card, then unplugging the card reader.

Restart the Mac mini, re-connect the card reader and re-insert the SD card.

If it looks the same select the OWC Card Reader Media and post another screenshot please.

How are you formatting the 32GB memory cards...?

What are you going to do with the 32GB memory cards..?

see > Erase and reformat a storage device in Disk Utility on Mac - Apple Support

Do the cards have something already on them?

Do they have other partitions or volumes on them?

Can you post a screenshot of Disk Utility, when you try to format the cards?