mkfs problem

[Pierre Frenkiel <pierre.frenkiel@gmail.com>]

hi,
I'm trying to fromat a nes USB flash drive and I get this:

==> mount | grep sdh

==> mkfs.vfat /dev/sdh1
    mkfs.fat 4.1 (2017-01-24)
    mkfs.vfat: /dev/sdh1 contains a mounted filesystem.

==> mkfs /dev/sdh1
    works

any explanation?

best regards,
--
Pierre Frenkiel