I pulled the hard drive from a *nix-based CCTV DVR so I could look at the contents and mount points, with the explicit intention of mounting a separate drive at the folder wherever the video is stored. I plugged it into an external dock and one 6 GB partition opened in Nautilus; GParted shows a larger unknown file system before the 6 GB volume. Is there a command I can run to discover the FS type of the unknown volume?
If the CCTV DVR is *nix based, it might have a filesystem you can know about; for that you may get some good results just running:
file -s /dev/xxx
on the device file of the partition. The fact you can open the second partition seems promising (there might even be data on the second partition as clues, like fstab entries).
However, depending on brand and vendor and such, it's always possible that the secondary parition is proprietary (not very common to invent a private filesystem though), or managed by a driver built locally on the DVR device, it could be a kind of logical partition created by the DVR firmware which embeds known filesystems within it, so gparted and such will only read the GUID partition table and not know anything more about the partition's contents. (More information may be available if you were able to post more detail about the DVR hardware and firmware, and possibly details about the known partition).