independently of other VMs. (The LUN had to move when the VM moved, which
meant that if other VMs were stored on the same LUN, those VMs would also have to
move.) With CSV, many VMs could be stored on a single CSV volume, with VMs
running throughout all hosts in the cluster. Behind the scenes, CSV still leverages
NTFS, but it controls the writing of Metadata to the volume to a single host for each
CSV volume to avoid any risk of NTFS corruption. This is also explained in detail in
Chapter 7.
With Live Migration and CSV technologies working in unison, the ability to move a
virtual machine between hosts in a cluster with no downtime was now possible and
removed a major obstacle to the adoption of Hyper-V. Windows Server 2008 R2
included other enhancements:
A processor compatibility mode that allowed a virtual machine to be migrated
between different versions of the same processor family. When a guest OS started
within a virtual machine, it would commonly query the processor to find out all of
the instruction sets available, as would some applications, and those instruction
sets would possibly be used. If a virtual machine was then moved to another host
with a different processor version that did not support that instruction set, the
application/OS would crash when it tried to use it. Download Coreinfo from:
http://technet.microsoft.com/en-us/sysinternals/cc835722.aspx
and execute it with the -f switch. This will show which instruction sets are
supported on your processor. When the processor compatibility feature was
enabled for a virtual machine, the high-level instruction sets were masked from
the VM so it did not use them, allowing the VM to be moved between different
versions of the processor.
Hot-add of storage to the SCSI bus. This enabled additional VHDs to be added to a
virtual machine without shutting it down.
Network performance improvements, including support for jumbo frames, Virtual
Machine Queues (VMQs), and allowing the use of NIC Teaming implemented by
network drivers
If the processor supported it, Second Level Address Translation (SLAT), which
allowed the processor to own the mapping of virtual memory to physical memory,
therefore reducing overhead on the hypervisor. SLAT is used by Hyper-V when
available.Windows Server 2008 R2 Service Pack 1
It’s not common for a service pack to bring new features, but Windows Server 2008
R2 had one key feature missing, and this was the ability to change dynamically the
amount of memory available to a virtual machine. SP1 for Windows Server 2008 R2
added the Dynamic Memory feature, which was different from how other hypervisors
handled memory optimization.