Spotlight on Hyper-V 3.0 high availability and redundancy

Microsoft has taken major steps toward improving Hyper-V 3.0’s high availability capabilities with the addition of predictive failure analysis and increased redundancy.

IT administrators face the critical task of ensuring the integrity and availability of network servers, the importance of which only increases with virtualization. Prior to the advent of server virtualization, a server failure typically affected only a single workload. A failed virtual host, however, may affect dozens of workloads -- resulting in a major outage.

Given the importance of high availability in virtual data centers, Microsoft Hyper-V 3.0 includes new features to spot potential errors and add redundancy.

New: Hyper-V 3.0 predictive failure analysis
Predictive failure analysis is a major improvement to Hyper-V 3.0. It allows the Windows Server 8 operating system to support native handling of error correction codes (ECC), which should reduce application downtime.

With ECC support, the OS system memory manager monitors memory pages and the takes the page off-line if the error count exceeds a predefined threshold. It also adds the page to the persistent bad page list, so it won’t be used again.

With Hyper-V 3.0, when Windows identifies a bad memory page, Hyper-V momentarily suspends all virtual machines. If the operating system can isolate the error to a single virtual machine, it shuts down the VM, marks the memory page as bad and restarts the VM. If the OS cannot trace the bad memory page to a single VM,  it resumes all virtual machines. In this case, the potential remains for a fatal error to occur if the page is accessed later.

Improved: Hyper-V 3.0 redundancy technologies
Microsoft also added redundancy to almost every level of Hyper-V 3.0 architecture. The previous version of Hyper-V offers two forms of node redundancy: live migration for planned downtime and failover clustering for unplanned downtime.  This functionality now supports Hyper-V 3.0’s larger clusters.

To ensure failures do not occur as a result of storage I/O problems, Hyper-V 3.0 includes an I/O redundancy feature through network interface card (NIC) teaming.  With this OS feature, administrators can combine multiple network adapters, providing additional bandwidth, load-balancing and failover capabilities.

Previously, Hyper-V NIC teaming was only possible with proprietary  hardware. With native, OS-level NIC teaming, it’s possible to mix and match NICs from different vendors and still ensure that if a single NIC fails, communication can continue through the remaining NICs. Additionally, Hyper-V 3.0 offers multichannel server message block (SMB) and  multipath I/O, which give the server more than one channel through which to communicate with the storage.

More: Hyper-V 3.0 replication capabilities
Hyper-V 3.0 also enables virtual machine (VM) replication, synchronously through integration with storage arrays, or asynchronously through the hypervisor.

In terms of high availability, both replication capabilities create working copies of virtual machines, which you can use if there’s an outage. Though reliable, synchronous replication is susceptible to network latency and is generally considered suitable only when a high bandwidth connection is available between two data centers located in close proximity. Conversely, asynchronous replication isn’t as sensitive to network latency offers much better performance, but it does have the potential for a small amount of data loss.

Hyper-V 3.0’s asynchronous replication capabilities promise to be a boon to cost-sensitive IT shops. Today, it is possible to create host server and virtual machine replicas at the storage level, but this hardware-based approach tends to be expensive and is not application aware. On the other hand, Hyper-V 3.0 replication will create application-consistent virtual machine replicas without the need for additional expensive hardware. This capability assists VMs running applications like Exchange Server because it allows the underlying databases to remain in a consistent state.

The Hyper-V 3.0 replication process also allows you to perform the initial replication either online, over the network, or offline, if you have a slow wide area network. The offline replication process entails the copying the VMs, shipping them to the remote site, loading them on your server and then replicating any changes that have occurred since the copies were originally made. This option reduces replication time for large VMs.

In addition, the replication process supports Windows-integrated and certificate-based authentication, which allow two hosts to mutually authenticate each other’s identity. The replication data also can be compressed and encrypt, which is essential to performance and security.

Overall, Hyper-V 3.0’s predictive failure analysis and redundancy will help ensure high availability --which, in turn, should reduce virtual machine and application downtime.

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