What Makes An NVR "Enterprise Class"?

This is a good discussion, one we have been having internally.

I would say that most of the standard specs like RAID support, over 16GB of RAM, and at least 10-15TB of usable storage would be minimum, and are available in many "non-Enterprise Class" NVRs.

If we're talking just a hardware based NVR (separate from the VMS software package), I would generally expect dual power supplies for redundancy, a dual Xeon processor option, and the ability to monitor the server hardware from a central management software (Dell OpenManage, HPE Insight, etc). I would even consider including VMware, or Hyper-V support, but that's stretching it a little if we're just talking about recording video.

Its a much larger picture and discussion once we get into software features of any specific VMS.

A simple start would be the management of devices, users and options across multiple units across multiple time zones and network configurations.

As an example, if you have a USER who can access many devices you should be able to restrict, enhance or remove from a single setting or by the use of LDAP or Active Directory. 

If you are searching video you should be able to define the TIME SELECTION across multiple time zones.  I need to see the front doors at 8:00 am in Germany, China and Canada.

An input from one site should be able to trigger an output from another, anywhere in the connected system. (Global I/O)

and more.

To me the starting point is making sure the device has more than 1 network connection, which makes it easer to create a subnet with the cameras and only link 1 device to the main network.

A pretty good list in here so far.  Here is a few more:

- SNMP MIBs

- Failover

- 3-5 year next business day parts warranty

Along with what everyone else has commented, having Active Directory integration would make it enterprise. 

From a hardware perspective, I'd want dedicated out-of-band management like iDRAC or iLO (vendor dependent), ability to have a recovery partition, support for SSDs in separate bays, redundant power supplies, 4 x GigE NICs, able to operate in a 'lights out' mode, a UEFI instead of BIOS, and support for any/multiple RAID types. While many 1U servers are powerful and have all these features, they typically cannot accommodate full-height plug-in cards - for example if I want to add an encoder card to support a mix of IP and analog cameras (still gotta do this on some take overs), I'd need a 2U server.