Hyper V on Win Server 2012 throwing false out of space alerts and then intermittently pausing VM's (When Veeam runs)

Question

I have a Windows Server 2012 R2 machine running Hyper V with 6 virtual machines on it. My issue is each of the machines have a status saying they are running out of disk space.  Neither of the hard drives on my host are low and none of the VHD's are
low...which as long as they work, not a big deal. The issue that we're running into is when Veeam runs backup jobs some of my VMs will pause. The odd part is we might have 2 to 5 of the 6 machines pause maybe once a month, so it's not happening consistently.
We've contacted Veeam support and they've been useless, they advised we upgrade to Veeam 8 which made no change. We have a number of other virtual hosts with virtual machines being backed up by Veeam that never have this issue... Is this a Hyper V issue or
a Veeam issue? Any advise would be appreciated!

Answer 1

My boss had worked with Veeam on this issue and they tried an upgrade to resolve this, however, it's happened again a number of times in the last week. I went through my logs and I also looked at my storage (Posted below). The servers that paused today are (App4,
FS3, FS4, FS5). App3 and FS1 have also paused before, however, not this time. Phone1 has not paused. So our total usage is 2.2 TB of a 2.45 TB drive. All the VHD files are stored on the virtual host D drive. I'm not understanding the status warnings, some
say they are running out of space when there is indeed enough space on both the VHD files for C’s and D’s.
I reached out to a vendor/contactor we use for complex issues and I posted his advise below, however, it's not making sense to me... We do not use snap shots and as of this moment we're not at a low space threshold. Is the issue as simple
as we have too much on this server and the Veeam backups are triggering the host's D drive to go below the low space threshold?
"When I setup virtual servers, I setup fixed disk and fixed memory usage, this keeps the memory cache from fluctuating and I limit the disks to only what the server needs and then expand them as needed. Fixed disk perform
better and it is a good way to avoid fragmentation and out-of-control dynamic disks. At this point, your issue is going to be freeing up space on the D: drive of the Hyper-V server – your snapshot logs (and possibly someday replication change logs) are going
to continue reach the disk space limit. There are some registry changes that some suggest to disable the safeguard, but remember, this is a safeguard as the server need free space on the Hyper-V server host to operate."
Server Specs
App3 - Dynamic - C: 47.36 GB used of 50 - D: 250 GB used of 250 - No status warning
App4 - Dynamic - C: 193.12 used of 200 - D: - Disk running out of space
FS1 - Dynamic - C: 55.4 used of 100 - D: 1000 used of 1000 - No status warning, however,  the D drive is out of space?
FS3 - Dynamic - C: 55.62 used of 60 - D: - No status warning
FS4 - Dynamic - C: 19.1 used of 60 - D: 32.19 used of 100 - Disk running out of space
FS5 - Dynamic - C: 18.44 used of 127 - D: 74.04 used of 127 - Disk running out of space
Phone1 - Fixed - C: 127 - No status warning
Event Errors...
'FS5' has been paused because it has run out of disk space on 'D:\VM Drives\FS5\'. (Virtual machine ID 15D4F67C-562A-4AB6-AB72-47E8722CCB85)
'FS1' has been paused because it has run out of disk space on 'D:\vm drives\FS1\Virtual Hard Disks\'. (Virtual machine ID 304B2CAE-C9D2-401E-970B-F75874F6CF08)
^FS1 was not paused when I went in to start them this morning...