VDI issues: How to use SSD to improve performance
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When traditional spinning disk arrays came up short on performance for its virtual desktop infrastructure, Minneapolis-based law firm Lindquist & Vennum switched to a hybrid array from Nimble Storage Inc.
The hybrid storage array has performed so well that, in addition to the virtual desktop infrastructure (VDI), it handles almost all of the law firm's business-application servers and its Voice over Internet Protocol (VoIP) phone system, the firm's systems engineer Derek Schostag said.
Schostag said that the law firm initially deployed VDI running Windows 7 desktops on VMware Inc.'s View 5.1 using one Dell Inc. EqualLogic PS6500 array with 16 15,000-RPM Serial Attached SCSI, or SAS, drives.
Lindquist's users typically run Microsoft Office applications, Web browsers, personal applications, such as Pandora Radio, and litigation and e-discovery support applications, such as AccessData Group LLC's Summation. "We started out with one [array] and then we realized it [didn't have] enough capacity-wise as well as performance-wise, so we bought another [EqualLogic] array just to handle that," Schostag said.
But adding the second array didn't solve the problem. So, Schostag looked for another solution. He considered acquiring yet another EqualLogic array because his team was comfortable with the system. He also looked at solutions from EMC Corp., but he said that required too much space and complexity.
Schostag came across Nimble during his research. Nimble's hybrid storage architecture and feature set intrigued him, but others in the law firm had reservations about dealing with a startup. He contacted Nimble-supplied references, and every one of them said Nimble lived up to its promises. "Which is kind of rare," he said, "because every vendor fudges a little bit."
Lindquist bought a Nimble CS240 array with 16 terabytes (TB) of usable spinning-disk capacity and 640 GB of SSDs. The firm also uses iSCSI over 10 Gigabit Ethernet, Cisco's B-series blade servers, and two Cisco Nexus 5010 switches in the Thompson Reuters' Eagan, Minn., data center where it houses its IT equipment.
Nimble's compression provided immediate benefit when the law firm installed it six months ago. "I took all those [virtual] desktops, 11.4 TB worth of virtual desktops, and moved them all in one week over to the Nimble [array]," Schostag said. "It went from 11.4 TB to 4.4 TB. So, somewhere we reclaimed  TB. Plus, we went from two arrays and 32 disks down to one Nimble array."
Schostag said he sometimes would get end-user calls about nonresponsive desktops when he used the EqualLogic arrays, but he has experienced no performance issues with Nimble. "We would have to do our antivirus updates at night," he said. "We had to provision desktops during off-hours. If we wanted to build a new [virtual machine] or clone a VM, we had to do it after-hours because it would just kill the array. Now we do it in the middle of the day. Nobody even notices."
Schostag partially attributes his high-performance statistics to the Nimble array's cache-hit rate, which he said is running around 75%. "So, it's getting the majority of its information from cache, the SSDs, instead of going to the [spinning] disks," he said.
Schostag said Nimble's compression allows him to use only about 35% of the capacity he would need without the data reduction. That allowed him to move most of Lindquist's servers onto the Nimble array. He is also planning to expand the storage capacity available to each desktop from a 16 GB limit to 40 GB.
Lindquist still has the two EqualLogic arrays, but Schostag plans to use them for applications that don't require high performance, such as archiving.