@isg
You can choose to show or hide RWFS in Mass Storage Mode. Go to Diagnostics Page>RWFS Settings. However when "Show in Mass Storage" is checked, it will show up as another 'Device with Removable Storage' the same as your 3597 and microSD do, as it is not seen as a conventional Logical Drive which would be in with your Hard Disk Drives. RWFS will also show as "Disk [number] Removable" in Windows Disk Management between the 3597 and microSD.

In the screenshot below GARMIN (H:) is a Logical Drive split off from my Win 8 partition to allow writing to it by patched MS & MI [because i have my system drives write protected]. GARMIN (L:) is the RWFS which always appears immediately following the unit if 'Show' is selected and the microSD, if inserted in the unit, showing behind it [sequence is 0:/, 1:/, 2:/ which is reflected by the ascending sequence of the Disk Nos and Drive letters assigned by Windows]:

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