VDI issues: How to use SSD to improve performance
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The University of Portland’s ambitious plans for using virtual desktops throughout campus ran into a snag when its storage failed to keep up with the high write IOPS requirements. The university’s IT staff solved the problem with a Whiptail Accela 6 TB all-solid-state drive (SSD) storage array.
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Disbury said one of the major hurdles to VDI was getting enough IOPS to handle boot storms when brining up multiple machines simultaneously. He quickly found out his NetApp FAS3000 filers with Flash Cache could not deliver enough write IOPS, especially if he is to reach his goal of 1,500 virtual desktops on campus.
“To deliver VDI in the way we wanted, we knew we would need something fast on the front end to feed into our back-end enterprise storage,” Disbury said. “When we started to roll out our pilot program, we found the NetApp filer would not be able to sustain the types of reads and writes we were looking for. NetApp is a quick filer, but we found that enterprise storage is optimized for reads and caching and not so much for the write side of things.”
He said his team tried to optimize performance on NetApp by adding as many spindles as possible with NetApp’s RAID-DP, “but there are just certain limitations based on the architectural design of enterprise storage.”
Disbury said he looked at larger, more expensive systems using flash from NetApp and other major vendors before the university’s VAR -- MCPc -- pointed him toward a Whiptail storage solution. The university installed a 2U Whiptail Accela array about three months ago and has been able to move ahead with the VDI program. Disbury said the university has about 250 virtual desktops in PC kiosks and labs, and it intends to expand VDI to nearly the entire university. The next phase will be to expand to administrative staff and faculty.
“Anybody who’s due for a computer refresh this year will get it,” he said. “We’ll probably be able to cover about 95 percent of the campus with virtual desktops.”
Disbury said the Whiptail storage array has been “fantastic” for the write capabilities for his VDI. Whiptail claims the all-flash system can generate 250,000 write IOPS and 200,000 read IOPS. Disbury realizes this is an optimal number, but he said he is impressed with the way Whiptail uses multi-level cell (MLC) flash. MLC drives wear out faster than the more expensive single-level cell (SLC) flash, but he said his MLC drives are standing up better than he expected and he hasn’t had a drive failure yet.
“With the Whiptail [storage] we’re looking at max of 250,000 IOPS, which obviously is in a perfect case with a perfect set of disks,” he said. “They’ll degrade over time but because of the translation and the way they do the reads and writes, that was one of the things I found to be most elegant about their solution – they’re not burning through those disks at the pace you would expect.”
Disbury said flash solved his storage problem, although he had to upgrade his network to keep up.
“At this point, IOPS are no longer the problem,” he said. “That’s traditionally been the issue.
We’re finding now that the network is the pinch point, so we have to upgrade the back-end infrastructure to support that.”
The university is upgrading to 10 Gigabit Ethernet between academic buildings and 40 Gigabit Ethernet to the core.
Disbury said he expects to add more flash for demanding applications.
“Eventually my goal is to use flash for anything that requires fast storage, even moving beyond VDI,” he said. “We’ll start looking at putting enterprise systems on it. The ultimate goal would be to put our database environment out there.”
The university still uses its NetApp filers for lower-tiered storage and has a NetApp FAS2000 as a backup target.
“We can have ultrafast storage on SSDs, so applications that need super-fast write performance will hit Whiptail,” Disbury said. “Anything that needs reasonable fast storage will hit the SAS drives on NetApp, and general storage will go to NetApp SATA drives.”