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Virtual desktops and storage

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Storage vendors focus on VDI

Besides the aforementioned virtual desktop infrastructure capabilities, VDI users are leveraging advanced array features, such as data deduplication and thin provisioning, to reduce the disk space required for VM images and user data. Because many NAS arrays support data dedupe, and desktop VM images and user data are file based, network-attached storage is a natural fit for VDI. A case in point is offered by Dave DePillis, manager of IT operations at Allied Cash Advance, a Miami consumer loan firm. He runs all of his clients on VMware View 3 and stores desktop images and user data on NetApp FAS2020 arrays. "We're not using linked clones at this point because of some limitations, but instead rely on NetApp's deduplication to preserve disk space. After deduplication, we gain back about 85% of the allocated storage," DePillis said.

As VDI capabilities like VMware's linked clone and Citrix Systems' equivalent feature in Provisioning Server mature, they'll be the preferred method of reducing disk space for virtual images because they provide the added benefit of having fewer desktop images to manage. Rather than managing one desktop image per virtual desktop, desktop management is reduced to managing one or a few master images. Patches, upgrades and configuration changes applied to the master image will be automatically propagated to virtual desktops

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that are linked to the master image. The impact on desktop management is huge and only compounded as the number of virtual desktops grows. "I hope to eventually be able to leverage VMware's linked clones to simplify patching and software upgrades; at that point the NetApp deduplication will mostly benefit user data," Allied Cash Advance's DePillis said.

VDI poses something of a storage paradox. It calls for relatively low-end storage to make the ROI work, but it also needs to be highly available. "Our customers say that they want tier 1 availability at tier 6 pricing for VDI storage," VMware's Sakac quipped. As a result, VDI deployments are likely to shy away from expensive Fibre Channel SANs and gravitate toward less expensive iSCSI SANs, a notion confirmed by Hewlett-Packard (HP) Co.'s acquisition of iSCSI pioneer LeftHand Networks Inc. in 2008. "Its built-in replication, support of thin provisioning and the simplicity of iSCSI make the HP LeftHand P4000 SAN a perfect fit for VDI," explained Lee Johns, director of marketing for HP's StorageWorks Division.

The larger the number of virtual desktop users, the higher the risk of network or storage contention. Most feared is the so-called boot-storm that occurs when a large number of users fire up their virtual desktops. With features like linked clones that cause many users to access the same virtual machine image on the same blocks and spindle, a serious performance bottleneck is inevitable unless the storage array has plenty of cache. So any storage array used for desktop VM images should have an option to add cache if needed. "All NetApp filers with PCI slots have the option of adding one or multiple Performance Acceleration Modules [PAMs]," explained Manish Goel, NetApp's senior vice president, product operations. At this time, each PAM can add 16 GB of read cache for a total of 80 GB. NetApp said future expansion will allow a maximum cache of 512 GB.

Gathering momentum

From maturing VDI products, impending offline capabilities, Microsoft's addition of a VDI session broker in Windows 7 and Intel's chip-side support for client-side hypervisors, to emerging VDI service providers that offer VDI as a managed service, the momentum behind VDI is gaining strength. Because of its infrastructure requirements and because it represents a radical change to managing desktops, wide adoption is all but certain. The stars are lining up behind VDI to cause a major change in how companies will manage desktops in the future.

 

BIO: Jacob Gsoedl is a freelance writer and a corporate director for business systems. He can be reached at jgsoedl@yahoo.com.

This was first published in August 2009

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