DR for virtualized servers


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Hypervisors and DR
With approximately a 70% share of the market, according to an ESG survey, VMware is the prevailing hypervisor, followed by Microsoft Virtual Server with 23% and about 4% for the various XenServer derivatives. By offering Hyper-V (the successor to Microsoft Virtual Server) as an integral part of Windows Server 2008, this market share ratio will likely change. "With a significant price advantage and the fact that Hyper-V is part of the operating system, we predict that within 18 months there will be more VMs running on Hyper-V than on VMware ESX," says ESG's Bowker.

Even though the different hypervisors are based on the same fundamental architectural principles, they vary in implementation and management capabilities. This impacts data protection and DR, requiring different approaches for implementing DR solutions.

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VMware ESX Server
At this point, ESX Server leads in features, performance and scalability, and has options and architectural characteristics that are beneficial for data protection and DR. To start, ESX Server doesn't run atop a third-party OS like Windows or Linux; it boots a very thin kernel optimized for the single-purpose hypervisor task without the overhead of a general-purpose OS.

It comes with Virtual Machine File System (VMFS), a clustered file system designed specifically for virtualization. Shared storage is a key requirement for hypervisors to share data across VMs and for live migration. "VMFS fully supports live migration, and enables multiple VMs to share a single LUN and still be able to migrate and fail over individual VMs," explains Noemi Greyzdorf, research manager, storage software at Framingham, MA-based IDC.

VMware's decision to opt for a proprietary file system and to perform storage management tasks makes it more challenging for existing data protection tools to back up and replicate virtual machine disk format (VMDK) files stored on a file system foreign to traditional tools. To overcome this challenge, VMware released a set of tools and apps that mediate between the proprietary VMware protocols and mechanisms and standard data protection applications.

With virtual disk files stored on a proprietary file system, ESX users need to run backup agents within each VM or sign up for VMware's Consolidated Backup (VCB) to provide for a more efficient and scalable backup solution with low impact on server performance. Consolidated backup takes a VM snapshot and mounts the snapshot to a central proxy server from where the data is backed up via regular backup apps.

This was first published in December 2008

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