I've used kernel 3.2.29 wich works fine with Hyper-V but When I tried to upgrade the Kernel it didn't boot because it didn't find the root partition, looking at dmesg I found out this:
ata_piix Hyper-v Virtual machine detected ATA device ignore set
So actually the ata_piix driver is ignoring my virtual partitions (I don't know why) and this happens only on 3.4+ kernels.
There is also no way to boot the virtual machine from a scsi disk so I can't even work around in that way.
Any idea on how I can tell the kernel to stop ignoring the devices ? My kernel il 3.8.13 now.