How ASIC stops I/O storms hurting its SANs

The Australian Securities and Investment Commission has deployed virtual desktop infrastructure, creating 3000 desktop images for its 2300 staff. At VMworld it explained how it runs that fleet without boot storms hurting its SANs.

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When staff come in to work Australian Securities and Investment Commission (ASIC) they are likely to find their thin workstation is already on, thanks to strategies that prevent VDI boot storms.

Boot storms, also known as I/O storms, are a SAN-halting phenomenon that can take place when many users all arrive at work and log on to a large fleet of virtual desktops. ASIC’s virtual desktop is 15 gigabytes and it has 2300 users.

One way ASIC avoids boot storms is to automatically boot up desktop computers at 5:00 AM on Monday morning, a time hardly anyone has reached their desk at the organisation’s 13 offices. As no-one is working, no-one will notice the performance hit the Commission’s SANs and networks experience at that time.

The Commission has also scheduled and randomised updates to its anti-virus application. As Australia’s regulator of financial institutions, ASIC’s work is sensitive enough that desktop anti-virus protection is a security necessity. In the pilot phase of its VDI implementation Technical Engineer Jeff O’Connor noted the anti-virus application’s hunger for SAN resources.

“We had assumed traffic would be 80 percent reads and 20 percent writes,” he told VMWorld 2011 in Las Vegas today. The reverse turned out to be true, thank in part to the anti-virus application initiating three writes to the SAN under certain conditions.

“Most anti-virus apps hammer the disk. We got hit at 2PM on a Thursday and 400 users went out for an afternoon,” O’Connor told VMWorld, explaining the reason for the staggered scheduling of anti-virus updates.

Even with those precautions, ASIC found its initial SAN specification could meet the input/output requirements VDI imposes.

“We had scoped SAN at a certain number of disks and found we had to almost double the disk count to get the IO we needed,” he said.

O’Connor also said the organisation tested extensively to determine the optimal LUN size for VDI, and settled on 300 gigabytes to support 20 virtual desktops. He said the organisation tries to use 90% to 95% of capacity on each LUN.

“This choice has never caused us a problem,” he told a sizable VMworld crowd. “I am a conservative guy and my name is on this project. I did not want any problems.”

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