Sizing your storage to support VDI is no easy feat. When Victor Community Support Services deployed VDI this year, IT director Jamie Rabenstein implemented a phased rollout to ensure consistent storage performance.
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The Chico, Calif., health services agency replaced a Dell EqualLogic SAN with a Nimble Storage SmartStack configuration with Cisco that runs Condusiv V-locity software for "smarter" Windows storage.
The Nimble CS-300 hybrid flash system is connected to a six-blade Cisco Unified Computing System (UCS) via 10-Gigabit Ethernet and top-of-rack Brocade VDX 6720 switches. Rabenstein said he kept the Brocade switches he was already using rather than take Cisco's recommendation to buy its competitive UCS fabric interconnect.
Two UCS blades handle 70 TB of production storage and four blades support an initial rollout of 270 virtual desktops. Condusiv software runs on the Nimble Storage SmartStack array to intelligently cache data in DRAM to prevent fragmented write requests.
Rabenstein plans to fill out the Cisco UCS chassis with two additional blades to support an eventual deployment of 800 virtual desktops. He estimates the full implementation will require up to 18,000 sustained IOPS, a fourfold increase from the 4,500 sustained IOPS the Dell EqualLogic could deliver.
Expected VDI advantages include cost savings, ease of use
The health services agency opted for VDI over laptop replacement for its 700 field clinicians at 22 sites in Northern California, Southern California and western Nevada.
"VDI is going to solve a bunch of issues for us: labor, money, longevity, ease of use, plus versioning for Microsoft Office," Rabenstein said. "We had been spending about $250,000 every year to refresh about one-quarter of our laptops. Our utopian idea for VDI is to buy less expensive gear and only replace it when it dies."
Victor Community Support Services used its EqualLogic iSCSI SAN for five years, along with four Dell PowerEdge R910 servers. The Nimble-Cisco UCS SmartStack configuration is the outgrowth of nearly a year's worth of experimenting. VCCS initially installed Condusiv Technologies' V-locity I/O Reduction software on the EqualLogic SAN to address split I/O related to multiple Microsoft SQL Server database requests. The agency ran V-locity in a testing environment for several months on the EqualLogic to set the baseline performance improvement needed to deploy large-scale VDI.
"During the daytime, our SAN would max out at about 4,500 IOPS," Rabenstein said. "After we put V-locity in, requests dropped to about 2,800 IOPS. So we did get a performance increase from the Condusiv [software], but we still needed an additional 16,000 to 20,000 IOPS for VDI."
Nimble architecture, V-locity software provide VDI headroom
VCSS considered Dell Compellent, EMC and NetApp storage hardware, as well as converged platforms from Nimble and Tegile. Rabenstein said Nimble's Cache Accelerated Sequential Layout (CASL) architecture was the deciding factor.
CASL uses several techniques to dynamically adapt flash to storage workloads. Hot data is cached in solid-state drives to accelerate read requests. Random writes are collected, organized and written sequentially to disk. CASL also compresses data as it is written to the array.
"All the other vendors required many, many more spindles. We needed more than fast reads. We need fast ingestion of data writes, and only Nimble could do that," Rabenstein said.
VCSS purchased UCS to run behind the EqualLogic as a repository when migrating storage to the Nimble Storage SmartStack. The agency replicates data nightly from the Nimble CS300 in the main data center to a Nimble CS460 array at a disaster recovery data center in greater Los Angeles.
The combination of Nimble and Condusiv V-locity reduced the load on switching associated with fragmented file requests. Even with VDI, Rabenstein said VCSS is able to achieve sustained IOPS of about 2,900 during peak demand, giving it sufficient room to add virtual desktops incrementally.
"Nimble would have made everything better, even if we didn't add Condusiv," he said. "The thing Condusiv does that Nimble can't do is make Windows understand that it needs to write smarter. As soon as we put them in together, our storage was like greased lightning."
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