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For some reason, Thunar will sometimes show LVM2 physical volumes as removable devices. As an example, with Ubuntu 12.04 and Xfce using an encrypted disk that then contains a LVM2 physical volume, that volume will come visible even when it isn't mountable. The solution involves using the UDISKS_PRESENTATION_HIDE environment variable. However, this needs to be passed to Thunar using udev.
Adding the following in /etc/udev/rules.d/99-hide-thunar-devices.rules will hide devices starting with “md” and ending with “_crypt”, essentially hiding encrypted raid devices.
Alternative syntax if you know the exact device name:
The bad news: a reboot seems to be needed.