For small businesses, there’s often no easy answer when it comes to disaster recovery. With many storage and DR options out of reach, finding an affordable way to protect data can be challenging. But in Hyper-V Replica, Microsoft offers a new path to DR for many SMBs.

Usage Scenarios

Hyper-V Replica, one of many operational and performance improvements to Hyper-V in Windows Server 2012, allows users to replicate virtual machines over slow, unreliable network links. Replica is purely a DR solution and doesn’t replace clustering, but it can be used to replicate clusters of Hyper-V servers.

With Replica, SMBs can set up a DR site at a branch office (or at a remote site hosted by a service provider) and use Hyper-V to replicate the contents of selected VMs at 5-minute intervals.

Unlike most enterprise-grade replication technologies, Hyper-V Replica does not require a reliable, high-bandwidth network link between primary and DR sites. It’s designed to work with links that don’t run over dedicated lines, such as broadband or asymmetric digital subscriber line (ADSL) technologies, which may be subject to short outages.

The Replication Process

To begin, Hyper-V Replica creates an initial copy of the primary server. That file is then copied over, either manually or over the network, to the Replica server at the recovery site. Replica then writes to a log file (Hyper-V Replica Log, or HRL) on the primary server every time there’s a write operation. This HRL file is replicated on the Replica server and is replayed every 5 minutes, in reverse, replicating only changes made since the last replay.

Due to the 5-minute replication frequency, if the primary server goes offline, up to 10 minutes of data might be lost. If Hyper-V can’t replicate at the 5-minute interval, an alert is written to the event log. If replication fails for more than 30 minutes, the Replica server is put into a failed state and replication must be manually restarted — so it’s possible that an hour of data could be lost at the DR site.

The replication schedule is designed to keep the state of the operating system consistent after a failover to the Replica server. If it’s critical that applications remain consistent, Hyper-V Replica can be set to create additional Volume Shadow Copy Service (VSS) recovery points for this purpose.

Ensuring Security with Hyper-V Replica

Before implementing Hyper-V Replica, Windows Firewall must be configured to allow the necessary replication traffic to pass through. This applies as well to any other firewalls that separate the corporate intranet from the DR site. Replica comes with default Windows Firewall rules, but they must be enabled manually in the Windows Firewall with Advanced Security management console. There are two inbound rules:

1. Hyper-V Replica HTTP Listener (TCP-In)
2. Hyper-V Replica HTTPS Listener (TCP-In)

The HTTPS rule is needed only if certificate-based authentication is used. Hyper-V in Windows Server 2012 also includes a new simple authorization model in which a Hyper-V Administrators group is created on each server that hosts the Hyper-V role. Hyper-V Administrators can configure Replica servers to accept incoming connections from specific Hyper-V servers.

There are two different types of authentication that Hyper-V Replica uses. Kerberos, a network authentication protocol, is the default option, but certificate-based authentication allows replication between primary and Replica servers to be encrypted.

Integrated authentication uses the Kerberos protocol and can be established between trusted Active Directory domains. In the absence of Active Directory, X.509v3 certificates can be used instead of Kerberos. Replication Authorization Tags protect Replica VMs residing on a single server in a data center, which is useful for hosting service providers that need to stop clients from gaining access to Replica VMs other than their own.

Installing Hyper-V Replica

Replica works in both workgroup and domain scenarios, and Replica servers don’t need to be in the same AD domain as primary servers. The first step is to configure a Replica server in a branch office by adding the Hyper-V role. This is done either with Server Manager or by using PowerShell. Once the role is installed, the server must be restarted. The following PowerShell command will install the Hyper-V role and management tools:

Install-WindowsFeature -Name Hyper-V –IncludeManagementTools

Now open Hyper-V Settings in the Actions pane of Hyper-V Manager, click on Replication Configuration and select Enable this computer as a replica server in the Details pane. Choose an authentication method, and don’t forget to enable the default Windows firewall rules. In the Authorization and storage section, the system can be set to allow replication from any authenticated server or from a specific list of servers.

VMs in the primary site can be enabled for replication with a simple wizard. In Hyper-V Manager, select a VM in the Details pane, right-click the VM and choose Enable Replication. The wizard allows a choice in how to perform the initial replication, which by default happens over the network. That may not be feasible or desirable over a slow network, so there’s also the option to perform the first replication using external media and then import the data at the Replica site.

Failover

Hyper-V has a new section in the configuration option for each VM called Failover TCP/IP, where both alternative IPv4 and IPv6 addresses can be provided should the DR site have a completely different IP addressing scheme than the primary site. These addresses are used when a failover action is performed.

There are three kinds of failover:

• Test Failover
• Planned Failover
• Unplanned Failover

A Test Failover allows Hyper-V administrators to perform a failover without disrupting the primary server.

A Planned Failover should involve no data loss; the primary server will temporarily become the Replica server for the VM that has failed over. The VM on the primary server needs to be shut down beforehand, and the primary server must be configured as a Replica server.

An Unplanned Failover is not expected and is initiated from the Replica server at the DR site. A VM on the Replica server will be started from a Replica recovery point. This could result in some data loss.

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With Windows Server 2012 (formerly “Windows Server 8”) on the horizon and many IT shops mulling upgrades, it’s more likely upgrades to Server 2012 will be incremental rather than all-at-once. It’s likely that those with infrastructure built on top of Windows Server will have both Server 2012 and older versions of Server running side-by-side for some time.

Given that, here are a few answers to common questions in this area how the new and older versions of Windows Server might have coexistence issues.

Can I run Windows Server 2012 systems in a cluster with earlier versions of Windows Server?

The small answer is “no.” There are several reasons for this, not least of which are the major improvements in the way clustering is managed and deployed across servers in Windows Server 2012. The new clustering features aren’t backward-compatible with earlier versions of Windows Server, so clusters can’t be upgraded in a “rolling” fashion; each node in a cluster has to be evicted from the cluster, upgraded to Windows Server 2012 and added to a total new cluster of 2012-only servers.

Here are some of the key new clustering features in Windows Server 2012, which will not be supported by earlier versions of the operating system:

Storage migration . This allows cluster-managed VMs to be live-migrated to a new place while the VM is up and running, in much the same manner as VMware’s vMotion.

Clustered shared volumes . This feature is not new to Server 2012 — it was introduced in Windows Server 2008 R2 — but it’s been revised and expanded, and the expanded functionality is not available for previous versions of Server. Multiple nodes in the same cluster can share the same file system, which allows a VM hosted on any node in that cluster to be migrated to any other node on that cluster.

Cluster-aware updating (CAU) . Updates to machines in a Windows Server 2012 cluster can be applied automatically in a rolling fashion. This way, the total cluster remains online during the process. Plugins that talk to an API expand CAU’s behavior.

There are many other new features, but to use them uniformly across a cluster requires a cluster-wide upgrade to Windows Server 2012.

What do I need to know in this area using file shares between Windows Server 2012 and earlier versions of Windows Server?

Windows Server 2012 uses the new SMB 3.0 protocol (originally SMB 2.2) for establishing file shares between Windows systems.

SMB 3.0 clients will always attempt to negotiate the highest possible level of the protocol with any peer it connects with, so if you establish a share between Windows Server 2012 and earlier versions of Windows Server, the connection will be negotiated according to whatever level of SMB is available on the other server. Microsoft TechNet blogger Jose Barreto has a post with a chart that spells out the highest grade of SMB available to a connection negotiated between any two editions of Windows.

SMB 3.0′s new features are only available to other Windows Server 2012 or Windows 8 systems. Some of the new features include:

Scale-out. The same folder can be shared from multiple nodes in a cluster for the sake of failover, surpass use of bandwidth, dynamic capacity scaling, load balancing and fault tolerance.

Multichannel help. Any multiple, redundant network associations between SMB peers can be used to accelerate the connection.

End-to-end encryption. Data sent between SMB 3.0 peers is encrypted by default.

VSS help. SMB shares are now covered by volume shadow copies as well, so data on file shares can also be backed up and restored owing to any VSS-aware software.

SMB Direct. Servers that use RDMA-capable network adapters can delight in high-speed memory-to-memory data transfers with far less CPU usage and latency than conventional copy operations.

SMB index leasing. This feature reduces latency for documents accessed via the Branch Cache feature, by locally caching more of the metadata associated with the document and reducing the amount of roundtrips to the original server.

Note that if you have a mixed infrastructure where all the clients and servers use SMB 2 or surpass — Windows Vista on the client side, Windows Server 2008 on the server side — disable the use of SMB 1.x with the PowerShell command Set-SmbServerConfiguration –EnableSMB1Protocol $fake. Disabling SMB 1.x reduces the potential attack surface for the server. If the protocol isn’t in use, it’s best to disable it to preclude a possible future exploit from being used on it.

What Windows Server features are being deprecated in Windows Server 2012?

Some features in Windows Server are no longer supported as of Windows Server 2012, or are in the process of being removed. Most of these deprecations only occupy code or applications that run directly on the new OS, rather than interoperations with other editions. That said, there are exceptions especially if, for instance, you have an older application that expects the same behavior when it tries to interoperate with the newer version of Server.

Here’s a list of some of the major deprecations and feature removals in Windows Server 2012 (with more listed at TechNet), which may impact cross-server compatibility or applications running on other servers:

Clustering. 32-bit cluster resource DLLs are being deprecated and must be replaced with their 64-bit counterparts whenever possible. Also, if you have any programs that use the Cluster Automation Server (MSClus) COM API, be aware that this API is now only available via an optional component named FailoverCluster-AutomationServer, which isn’t installed by default.

Databases. 16- and 32-bit ODBC help has been removed, as have ODBC and OLEDB drivers for Oracle and Jet Red databases. (Use vendor-supplied database connectors.) ODBC/OLEDB help is also being canned for any versions of SQL Server beyond 2000; for those editions of SQL Server and higher, use SQL Native Client instead. Finally, no version of SQL Server earlier than 7.0 is supported at all. It’s unlikely that anyone is still running SQL Server 6.5 or earlier, but any attempts to connect to a SQL Server 6.5 (or earlier) instance from Windows Server 2012 will breed an error.

Committed Index. Help for resource groups and using Committed Index Lightweight Index Services as an certification store have been deprecated.

UNIX. Many UNIX subsystem features are being deprecated or removed. Microsoft entire SUA POSIX subsystem is being deprecated, along with the line printer daemon protocol that is often used by UNIX clients. As a general replacement for Microsoft’s UNIX features consider using the Cygwin or MinGW, open source tools and APIs that are maintained entirely apart from Windows’s own evolution.

WMI. Many individual WMI providers are being removed or deprecated: SNMP (because SNMP itself is deprecated); the WMI provider for Committed Index (eclipsed by PowerShell), and the Win32_ServerFeature API.

Finally, the Windows Help application (winhlp32.exe) has also been removed although it has not shipped with Windows Server since Windows Server 2008. What’s more, no add-on version of the Windows Help program is being supplied owing to Microsoft as a download, as it did with previous versions of Windows that mislaid Windows Help. (Even if, a Windows Help journal for the client journal of Windows 8 will be made available later, which must do the job.)