Here is my setup: I am running a Dual Quad Core Xeon 2.0Ghz with 16GB of Ram and 2 x 2TB WD Green drives with FreeBSD 7 that has ZFS on root. The Hard Drives are in a ZFS Mirror. I am running VirtualBox 4.0.14. I have 2 Windows Server 2003 Guests that are each using 4 GB of Ram respectively and have 320 VDI Virtual Disks that are about 70% full. One Windows Server is a terminal server and the other is an MS SQL database server.
When performing disk copies and transfers from the FreeBSD server directly on Samba I am able to get 80-90 MB/s transfer rates on both read and write. When I try to transfer on inside the VM's I get a maximum of 10MB/s.
When I replicate a large file inside the VM I get 10MB/s max. Using zpool iostat I never see the VM's use more than 20-30 MB/s max transfer. Inside of VirtualBox configuration I have tried both the IDE adapter and also SATA. I have not tried SCSI yet.
What could be the causes of such slow disk access speeds?