Atlantis Computing unveiled Monday the first virtual desktop infrastructure implementation that does not use a storage appliance or disk array for storing and serving up virtual desktop images.
The company introduced Atlantis ILIO Diskless VDI, which works with Citrix Xen Desktop and VMware View virtual desktops. The technology is a software only-approach that runs as a virtual storage appliance and makes use of DDR memory on server blades.
Since much of the I/O performed by Windows is unnecessary in a virtualized environment, the Atlantis ILIO virtual storage appliance performs the I/O functions for all virtual instances on the server and controls the interface with the NTFS file system. Any unnecessary I/Os are not performed. In addition, by using VM-aware deduplication, the amount of storage needed for virtual images is reduced by 90%. Virtual image reduction allows more users to operate per GB of shared storage. This takes a very intimate knowledge of the disk access required by Windows, but the advantages of smaller virtual images extends beyond IO reduction to allowing more virtual instances per server
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In the diskless VDI implementation, each blade has an ILIO virtualized storage server that consumes 6 GB of storage. Another 160 GB is allocated to a RAM disk. With the VMware hypervisor taking 2 GB, the remainder of 320 GB of RAM is allocated to 160 virtual desktops. Eight blades can be aggregated into a 6U chassis, supporting 1,280 users, and a rack (30U) can accommodate 6,400 users. This is all accomplished within the servers, without the latency associated with accessing a storage appliance or hard disk drive or solid state storage array.
Many VDI implementations have been stalled at user organizations in the proof-of-concept phase because of the high cost and poor performance of shared disk storage systems. Disks in workstations and PCs typically cost $150/TB, compared with shared enterprise drives that cost upwards of $5,000/TB.
It would be just fine if a single drive could support hundreds of users, but it can't. On a good day, the shared drive can deliver 250 input-output operations per second (IOPS), while a typical Windows 7 user requires 25 IOPS. This means that an enterprise disk drive tops out at about 10 users. Adding more spindles causes shared storage costs to skyrocket by adding capacity that isn't really necessary to support storage needs of virtual workstations.
Telecommunications provider PAETEC (recently acquired by Windstream Communications) deployed Atlantis' ILIO based VDI software on Cisco Unified Compute System B230 M2 blade servers, which use Cisco's Extended Memory Technology to provide twice the amount of memory of conventional two-socket servers. The 512 GB of DDR RAM per blade server, with two Intel Xeon processors for a total of 20 cores, has plenty of capacity and horsepower to support 160 users directly out of high-speed memory.
Steve Bell, infrastructure systems architect for PAETEC, explained that, while flash memory installed on servers could deliver a lower cost per GB than the pure DDR implementation of the UCS blade servers, their overall fabric management capability within his telecom's environment more than offset any capital expense advantages by delivering lowered operating costs. PAETEC's resulting implementation yields a potential of 367 IOPS per user at a cost of under $200 per user. This is 15 times more IOPS than a high-end workstation can deliver, making the user experience much faster than in a conventional desktop implementation and resulting in desktop boot times of 12 seconds.
Deni Connor is founding analyst for Storage Strategies NOW, an industry analyst firm that focuses on storage, virtualization, and servers. Storage Strategies NOW's James E. Bagley contributed to this story.
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