I am truly at a loss and hope that someone can explain this problem to me. I have a SuperMicro server with 4 AMD Opteron 12 core processors. It also has 64gb of DDR3 ECC memory. It is running Windows Server 2012 R2.
I am running hyper v with 3 virtual 2012 servers and 1 linux proxy gateway. I also typically have a Windows 7 VM and a Windows XP VM running on this host. I have had 2 or 3 other Windows vms running at various times with no problem.
Just this morning I had an issue with the Linux gateway not running correctly. Eventually (with some help) I found out that the HD access speeds were dropping from 500-600 mb/s range to 10-30 mb/s range. I discovered this using DD command from the Linux command line. I began testing the HD speeds on the host using CrystalDiskMark and discovered that I was only getting somewhere in the range of 40-120 mb/s on the physical Hard Drives from the host OS. Keep in mind that I am using standard Sata drives 7200rpm.
What I don't understand is how I could be achieving better speeds on the VM than the host OS can get.
Also, I don't understand what could be causing the rate drop in the VM. The one thing I discovered is that the Linux VM seemed to hold its higher speeds until one of the Windows Server VMs was turned on.
I also purchased a new Sata drive and installed it and discovered that I was getting about 50-75% better transfer rates on that using CrystalDiskMark from the host. I honestly expected a much bigger increase than that.
After the single Windows server VM was completely started up I reran the tests on the host drive that contains both VMs and I got a range of 90-120 mb/s. I then ran a test on the Linux VHD using the DD command and it was now back up in the 400-500 mb/s range. I also ran the same CrystalDiskMark test from inside the Windows Server VM and was getting 130-150 mb/s range.
I'm just looking for some kind of explanation for what might be going on here. I have been running VMs on these types of HDs for years and have never had these kinds of issues. Could there be something else going on here?
If you don't have one that does caching ,performance in the VM world will suck.