The Ohio Department of Developmental Disabilities (DoDD) faced a big decision about its PC infrastructure 18 months ago. It either had to replace 80% of the agency’s desktops because they were between 4 and 7 years old, or move to VDI. Brian Brothers, DoDD’s network administrator manager, found a VDI implementation would be cheaper, and he went with VMware View because it is a VMware shop.
“As a cost savings measure, it was actually more affordable to switch to VDI and buy $200 thin clients instead of $500 to $600 PCs,” said Brothers.
Brothers said he found that figuring the cost per desktop was easier than calculating how many IOPS he needed for the VDI implementation.
“From our deployment and my understanding, the most important thing to look at is your IOPS from a storage perspective,” Brothers advised. “Obviously, you have to have enough space to hold everything, but it’s better to account for the numbers of IOPS first and then scale out if you need additional storage by adding disks.”
Brothers said for his Ohio DoDD VDI implementation of VMware View, he used the high end of what the vendors and other administrators suggested, which was between 40 IOPS and 80 IOPS per user. “I’d rather have the speed and not use it than not have the speed and need it,” he said.
“Ultimately, what we decided to do was put the majority of our I/O requirements on a solid-state SAN,” he said.
The DoDD bought two Whiptail Tech Virtual Desktop XLR8r SSD SANs -- a 6 TB SAN for the primary data center and a 3 TB SSD SAN for the disaster recovery (DR) site -- to tackle his high IOPS requirements.
The DoDD already had a Dell Compellent SAN with 110 TB usable capacity in the primary data center, and it replicates to another Compellent SAN with 78 TB usable capacity at the DR site. The SSD SAN handles the majority of the VDI I/O requirements, including most of the desktop boot needs, and the Dell SANs handle bulk-storage requirements.
Brothers said he was worried about his storage system becoming the bottleneck when he implemented VDI, but his early testing of the Whiptail SSDs alleviated his concerns. He said he was getting upward of 230,000 IOPS out of the SSD SANs, which far exceeded the VDI requirements based on the number of planned virtual desktops.
Brothers said the DoDD avoids typical VDI boot storms by rarely shutting down the VMs used for the virtual desktops. So when users log in to the network, their desktops are already booted and waiting. The potential login storm is no different from the scenario when users logged in to desktop PCs.
Brothers ran into trouble at first when he ran deduplication on the Whiptail SANs, as it slowed the SSD performance by 50%. So he stopped using the deduplication software and instead used the single-instance technology included in his Unidesk Corp. virtual desktop management software. The Unidesk software sits between the hypervisor and operating system, and Brothers said it helps reduce capacity required to run applications for the virtual desktops.
This was first published in November 2011