the previous requirement to use iSCSI or virtual Fibre Channel to enable shared
storage within virtual machines for guest clustering purposes.
Resource metering was introduced in 2012 Hyper-V for processor, memory, and
network, but not storage (other than the amount of storage used). In Windows Server
2012 R2, the resource metering is expanded to give more detail on the I/O profiles of
storage, including average IOPS and data read and written. 2012 R2 also allows QoS to
be used with storage to restrict the maximum IOPS of each individual virtual hard
disk and also can alert administrators if the IOPS drops below a certain threshold.
MOBILITY AND AVAILABILITY
Live Migration in Windows Server 2012 may seem to be the perfect solution, covering
all scenarios, but in 2012 R2, it has been made more efficient. The Windows 2012 Live
Migration method of copying memory over the networks specified for Live Migration
is still available in 2012 R2. However, the default now utilizes compression, which
reduces the amount of data sent over the network, thus reducing Live Migration
durations potentially by a factor of five at the expense of some extra CPU cycles to
both compress the memory at the source and decompress at the target. Another
option is to utilize SMB Direct as the transport. This may not seem like a good option
initially, but the goal is to use it if the network adapters support remote direct
memory access (RDMA), which allows it to be used; SMB Direct will be faster than
even compressed Live Migration, but it uses almost no CPU. Windows Server 2012 R2
also allows Live Migration from Windows Server 2012, which allows organizations to
migrate from 2012 to 2012 R2 without downtime for virtual machines.
Hyper-V Replica is also enhanced to allow different choices for the frequency of the
asynchronous replication of the storage changes. The 5-minute frequency from
Windows 2012 Hyper-V is still available, but additional options of 30 seconds and 15
minutes are also now offered (see Figure 1.8). Extended Hyper-V Replica can be
configured, allowing a replica to be created of a replica. Note that the extended replica
is sourced from the existing replica and not from the original virtual machine. This is
a useful capability for organizations using Hyper-V Replica within a datacenter who
also want an additional replica in a separate datacenter for true DR.
Figure 1.8 Extended Hyper-V Replica allows different replication intervals between
the replicas