We're a small shop, running a Dell T420 (dual CPU, only one present, 6 cores) w/32GB RAM as our main server. We have only 5 VMs, one of which is our WSE 2012 DC.
From time to time, and at a rate for which we've not been able to establish a reliable pattern, all of our VMs concurrently spike to 100% CPU. The host remains quiet at 4-5%. A host warm boot doesn't provide relief, but a cold boot at least puts things back in the box until the problem reoccurs.
Sometimes we can get a week or more of calm seas out of it; sometimes only a day. An unreliable pattern seems to be that it kicks off sometime during an extended idle period, i.e. overnight. An examination of the server's temperature logs first led us to suspect overheating, but further investigation into recent incidents have spoiled that lead.
We also found descriptions of similar problems on the Dell forums, with claims of resolution by installing the latest round of Dell updates. We recently engaged in a project to do just that (as an aside, it was quite an adventure getting ~700GB of VHDs safely off of and then back onto that machine), but to our utter dismay it didn't help.
We're absolutely befuddled. So is Microsoft support (or at least first tier support is, even though they try not to act like it). I'm including below our SystemInfo output.
Does anyone know where to start looking?
Host Name: SERVER1 OS Name: Microsoft Hyper-V Server 2012 R2 OS Version: 6.3.9600 N/A Build 9600 OS Manufacturer: Microsoft Corporation OS Configuration: Standalone Server OS Build Type: Multiprocessor Free Registered Owner: Windows User Registered Organization: Product ID: 06401-029-0000043-76293 Original Install Date: 4/3/2014, 4:07:15 PM System Boot Time: 5/4/2014, 1:56:47 PM System Manufacturer: Dell Inc. System Model: PowerEdge T420 System Type: x64-based PC Processor(s): 1 Processor(s) Installed. : Intel64 Family 6 Model 45 Stepping 7 GenuineIntel ~2200 Mhz [Intel(R) Xeon(R) CPU E5-2430 0 @ 2.20 GHz] (manually added) BIOS Version: Dell Inc. 2.1.2, 1/20/2014 Windows Directory: C:\Windows System Directory: C:\Windows\system32 Boot Device: \Device\HarddiskVolume1 System Locale: en-us;English (United States) Input Locale: en-us;English (United States) Time Zone: (UTC-09:00) Alaska Total Physical Memory: 32,723 MB Available Physical Memory: 12,716 MB Virtual Memory: Max Size: 37,587 MB Virtual Memory: Available: 17,129 MB Virtual Memory: In Use: 20,458 MB Page File Location(s): C:\pagefile.sys Domain: OIT Logon Server: \\SERVER1 Hotfix(s): 31 Hotfix(s) Installed. : KB2843630 : KB2862152 : KB2868626 : KB2876331 : KB2883200 : KB2884846 : KB2887595 : KB2892074 : KB2893294 : KB2894179 : KB2898514 : KB2898871 : KB2901101 : KB2901128 : KB2903939 : KB2904266 : KB2908174 : KB2909210 : KB2911106 : KB2913760 : KB2916036 : KB2917929 : KB2919394 : KB2919442 : KB2922229 : KB2923300 : KB2923768 : KB2928193 : KB2928680 : KB2930275 : KB2939087 Network Card(s): 3 NIC(s) Installed. : Broadcom NetXtreme Gigabit Ethernet Connection Name: NIC1 DHCP Enabled: No IP address(es) : Broadcom NetXtreme Gigabit Ethernet Connection Name: NIC2 DHCP Enabled: Yes DHCP Server: 192.168.1.12 IP address(es) : 192.168.1.135 : fe80::915b:8de0:712e:29f1 : Hyper-V Virtual Ethernet Adapter Connection Name: vEthernet (External NIC 1_Internal) DHCP Enabled: No IP address(es) : 192.168.1.11 : fe80::2d35:f582:4958:9eb2 Hyper-V Requirements: A hypervisor has been detected. Features required for Hyper-V will not be displayed.
== EDIT ======================
I've found the solution to this issue; I waited for over a year to make sure we didn't encounter any more instances of the problem.
Moderators: I'd like to request a reopening of the question, so that I can post the answer.