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  1. Downtime isn't so bad.

some vendors claim they can migrate data without causing any downtime for applications. But some observers, such as Gary Fox, director of national services, data center and storage solutions at Dimension Data, recommend building in some downtime because it's tricky to migrate data and ensure its consistency while doing a migration during regular production hours. If possible, he suggests, do migrations during non-business hours "so you're not under so much pressure" in case something goes wrong.

"I'm kind of old school in this regard," he adds.

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Managing migration in virtual environments
Server virtualization can make data migrations more of a challenge, with the prospect of migrating virtual machines (VMs) among physical servers, as well as migrating the data the VMs use. The system images, and the data needed by applications, may also have to be converted into new formats for use in the virtual environment.

Both virtualization vendors and third parties provide tools to perform such functions. VMware Inc.'s Virtual Machine File System (VMFS), for example, gives multiple VMs shared access to pools of clustered storage and, says the company, provides the foundation for live migration of virtual machines and virtual disk files.

VMware's VMotion also allows customers to perform live migrations of multiple VMs among physical servers with no downtime. It also provides management capabilities such as the ability to prioritize migrations to ensure that the most important VMs have the computing and network resources they need. VMware's Storage VMotion allows customers to migrate the data used by VMs among arrays with no downtime, but requires more manual work than is now required with VMotion, says Jon Bock, senior manager of product marketing at VMware. Either VMware, or storage vendors writing to VMware's API, will provide more automation tools for Storage VMotion in the future, he says.

Microsoft Corp. doesn't offer live migration of virtual machines in the initial release of its Hyper-V server virtualization technology, but says that capability will be included in the next release, which isn't expected until next year.

VMware recently announced vStorage, which includes new APIs designed to enable storage vendors to give their storage management tools better visibility into and integration with the VMware virtual environment, and to provide better visibility through the VMware vCenter Server management interface into how VMs are using storage.

VMware recently unveiled updates for Storage VMotion such as the ability to migrate volumes from thick- to thin-provisioned devices, to migrate data from Raw Device Mapping volumes to Virtual Machine Disk Format (VMDK) volumes, and to better integrate storage management into the VMware vCenter Server management interface.

The latest release of Symantec Corp.'s Backup Exec provides support for heterogeneous migration and replication of data in both VMware ESX and Microsoft's Hyper-V environments, says the company. Other third-party offerings include DataCore Software Corp.'s "Transporter" option for new licenses of its SANmelody and SANsymphony software that allows administrators to migrate disk images and workloads among different operating systems, VMs and storage subsystems.

Among other updates to its backup software, Hewlett-Packard Co. recently extended the Zero Downtime Backup and Instant Recovery features of its Data Protector software for VMware VMs, giving customers "zero impact backup of mission critical application data residing on virtual machines," according to the company.

This was first published in November 2008

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