Windows Server 2012 has been launched by Microsoft, including the latest incarnation of their virtualization platform Hyper-V. The new version of Hyper-V includes many significant improvements in scalability and availability. Some of the most intriguing changes are storage-related enhancements that offer robust features previously available only to organizations with large IT budgets. In particular, I will focus on advances related to Live Migration, Hyper-V Replicas, SMB 3.0 storage, and live snapshot merges.
The 2012 version of Hyper-V introduces a powerful new Live Migration wizard with some much needed improvements. Chief among them is the innovative concept of “shared-nothing” Live Migrations. This designation is based upon the fact that the new flavor of Live Migration does not require shared storage or cluster membership; it only needs an Ethernet connection between two Hyper-V servers in order to work. In this scenario, virtual machine files can be copied between two stand-alone Hyper-V servers using local storage, two disparate Hyper-V clusters, or even a stand-alone Hyper-V server and a cluster. Then, the Live Migration copies the memory, device state, and storage handles of the running VM from one Hyper-V server to another and hands it off with zero downtime. This type of migration eliminates storage dependency limitations. The requirements for this functionality are as follows:
- Hyper-V servers must be running on Windows Server 2012
- Servers must be members of the same domain or domains with a two-way trust
- Processors must be from the same manufacturer (Intel or AMD)
- Virtual machines must be configured to use virtual hard disks or virtual fiber channel disks (no pass-through disks)
- A dedicated management network of 1 Gbps or faster is recommended for Live Migration traffic
Microsoft should be applauded for introducing this game-changing migration functionality to the virtualization landscape. However, Microsoft’s monopoly on shared-nothing migrations is expected to be short-lived. VMware, the industry leader in virtualization, is expected to announce this capability as part of its vSphere 5.1 suite at VMworld 2012 this week. The next release of Citrix XenServer, the third most adopted virtualization platform, will also offer a shared-nothing migration feature during this quarter.
The new Live Migration wizard also offers a live storage migration option. This nuance is very similar to the shared-nothing migration except it only involves syncing virtual machine files from one storage platform to another while the running VM remains hosted on the same Hyper-V server. This differs from the Windows Server 2008 R2 version of Hyper-V that required the VM to be shut down before moving files to a new storage location.
Windows Server 2012 Hyper-V makes another storage-related leap forward with its Replica feature. With Hyper-V Replica, administrators can replicate their virtual machines from one Hyper-V host at a primary site to another Hyper-V host at a secondary site. This feature brings enterprise disaster recovery capabilities to small and medium-sized organizations that cannot afford SAN-to-SAN replication. Hyper-V Replica employs asynchronous replication designed for low bandwidth, high latency WAN connections. Replica servers can use HTTP and Kerberos for replication within a forest or HTTPS for inter-forest or hosted replicas.
Figure 1 – Hyper-V Replicai
The Hyper-V Replica feature is activated by the Enable Replication wizard. The wizard allows administrators to choose which VHDs to replicate, whether or not to use compression, and what medium to use for initial replication (over the network, external media, or a restored VM copy already present on the replica server). Once the initial synchronization is complete, only changes are replicated across the wire via log shipping in five-minute increments. Like shared-nothing migrations, Hyper-V Replica is completely storage agnostic and can be performed between any combination of stand-alone and clustered servers.
As great as these new features are, we need to offer an admonition. None of these features should be considered substitutes for the high availability offered by Hyper-V failover clustering. Live Migrations are useful when an administrator is proactively moving VMs to perform maintenance on a host, but not when reacting to a failure. The asynchronous nature of Hyper-V Replica makes it an inadequate HA solution, as well. Latency could cause a replica VM to be out of sync for up to an hour, which would likely mean significant data loss in a failover scenario. Failover clustering is the only way to quickly recover from a hardware failure without losing any data.
SMB 3.0 Shared Storage
In my previous blog, I discussed the new storage features introduced by SMB 3.0 in Windows Server 2012. One of the products that benefits most from these storage enhancements is Hyper-V. This product can now use SMB 3.0 file shares as shared storage for virtual machine files as an alternative to block-level storage mediums like fiber channel and iSCSI. This improvement delivers storage flexibility akin to VMware offering NFS as a file server protocol for connecting to datastores.
Figure 2 – Hyper-V using shared SMB storage on a large scaleii
Now, storage mapping for configuration and VHD files can simply be a UNC path (\\FileServer\Share), which will remain constant. A dedicated Gigabit or 10GigE Ethernet fabric for storage is recommended to ensure robust connectivity between Hyper-V servers and file servers.
Live Snapshot Merge
When a virtual machine snapshot is created and deleted in the Windows Server 2008 R2 version of Hyper-V, it does not merge out and delete the snapshot differencing disk file (.avhd) that was used for the snapshot until the virtual machine is powered off. Each time a snapshot is created, there is downtime incurred regardless of whether or not the changes are kept or discarded. The downtime required can be significant if the differencing disk file grows too large. In some cases, unchecked snapshot file growth can lead to running out of disk space on the Hyper-V server. Microsoft has addressed this shortcoming in the new Hyper-V with the introduction of Live Snapshot Merge. Now, Hyper-V will merge changes while a VM is running and no longer requires any downtime. The only impact administrators must consider is the increased disk I/O caused by the merge.
The innovations in Live Migration, Hyper-V Replica, SMB shared storage, and live snapshot merges demonstrate that Microsoft has made enormous strides in their drive to establish Hyper-V as an enterprise-class virtualization platform. Whether or not they are able to gain ground on VMware and Citrix remains to be seen. Nevertheless, the real beneficiaries of these efforts are the small and medium-sized organizations that will be able to leverage these enterprise capabilities for the first time. How prepared is your organization to exploit the benefits of Windows Server 2012 Hyper-V? Have you evaluated the licensing impact of a move to Windows Server 2012? Are you considering a migration from the VMware 3.x or 4.x and need additional information or real world expertise? Credera has extensive experience in designing, planning, and implementing IT infrastructure solutions. If you have questions about this blog post, points of view, or IT infrastructure, please contact us.
i TechEd 2012, Enabling Disaster Recovery for Hyper-V Workloads Using Hyper-V Replica, Vijay Sistla
ii TechEd 2012, Hyper-V over SMB: Remote File Storage Support in Windows Server 2012 Hyper-V, Jose Barreto