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How to prevent VDI boot storms without adding storage

VDI boot storms and logon storms are inevitable issues that can be fixed without throwing a lot more storage at the problem. Meanwhile, antivirus storms can be avoided altogether.

People say that virtual desktop storage has to be robust enough to support "storms" -- boot storms, logon storms...

and antivirus storms, which all impact virtual desktop performance. But throwing more storage at these storms isn't necessarily the answer.

Boot storms and logon storms sound the same, but they are different problems with different solutions. While those two storms are inevitable, the antivirus storm is avoidable.

VDI boot storms
Of the boot and logon storms, the boot storm is the easiest to handle. Boot storms are when many virtual machines (VMs) boot at the same time. Since boots are read-intensive operations, they're relatively easy to solve.

If you have a high-end storage system, it likely supports caching and can essentially keep the most used bits in memory, rather than physically getting the data off the disks. Often times that alone is enough to avoid a boot storm.

If you don't have a solution that can cache the data, you can still avoid boot storms by pre-starting your desktops in groups or "waves" a few minutes apart in the morning so that all the machines are ready for people to log on when they arrive. After all, you're storage is built to handle the general workload -- it's only when multiple people boot an entire OS that causes problems.

VDI logon storms
The harder of the two is the logon storm (or login storm), which occurs in spite of your best efforts dealing with boot storms. That's because logon storms, unlike boot storms, are write-intensive. Each user is doing something different, so the operations are unique. That means that it's more challenging to cache or optimize.

You can see how boot storms are comparatively easy to deal with. You can pre-boot your machines at various times throughout the night, but you can't tell your employees to come into the office at staggered times just to avoid logon storms.

This means that when planning out a storage solution, you need to pay more attention to logon storms than boot storms. It's not that boot storms aren't important -- it's just that there are more ways to deal with them than simply throwing more IOPS and bandwidth at the problem.

Antivirus storms
Boot and logon storms are inevitable consequences of storing desktops in the data center. The other storm, the antivirus storm, is more of a self-inflicted wound than an unavoidable gotcha.

In this case, admins tend to carry on business as usual by installing antivirus software into their VM image. While that isn't the end of the world by itself, they forget to take into consideration the fact that the default settings typically call for scheduled AV scans. Imagine the issue when all of your desktops start scanning their file systems at the same time!

It's easy enough to avoid this by tweaking some settings or turning off antivirus  altogether, but there are out-of-band or VDI-aware antivirus solutions available, too. No matter what, common sense will help you avoid the antivirus storm.

Read more from Gabe Knuth

Gabe Knuth is an independent industry analyst and blogger, known throughout the world as "the other guy" at He has been in the application delivery space for over 12 years and has seen the industry evolve from the one-trick pony of terminal services to the application and desktop virtualization of today. Gabe's focus tends to lean more toward practical, real-world technology in the industry, essentially boiling off the hype and reducing solutions to their usefulness in today's corporate environments.

This was last published in December 2011

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I agree that most high end systems can keep the desktop VM in level 1 cache to provide very fast performance and deliver the required IOPS for a boot storm and login storm. ZFS does a great job of caching and caching VM's for VDI.

However, I am not sure if you rely on sequencing waves of boots it will always be ok if you don't have enough total capacity for the max IOPS swings. If you have a crash in the middle of the day or some emergency which requires an immediate patch and boot you will have to have enough resources to handle rebooting all of the VM's in a reasonable amount of time. If you are doing controlled waves where you take 1/4th the VM's down and reboot and then the next 1/4th I can see it being ok. But, if you have an unexpected crash where everyone goes down and every VM has to be rebooted that could take hours and leave some users frustrated. I suppose it all comes down to how tolerable you are of downtime.
Great article and just goes to show that tools like Liquidware Lab StratusphereUX are key to really understanding what’s going on in your VDI environment. How do you indentify what is the root cause of the issues described in this post? StratusphereUX gives you key metrics up and beyond what your standard infrastructure monitoring tool can provide. Can standard tools demonstrate metrics like “logon time” or “application response” or “diskIOPs” all in the same solution? Not often but StratusphereUX does. Ricky El-Qasem Tech Director @ Liquidware Labs.
Nice article.
You are right. bootstorm is easy. Logon and log off storm is also contoleable with third party tools (appsense etc..) antivirus solutions are integrating with VDI by "off loading" antivirus (vShield, MCafee MOVE etc..). Let see wats next...
Easiest way to solve these IO issues and to simplify your VDI deployment is to implement VDI on cost effect MLC solid state storage solution. Whiptail Tech, Violin Memory and Pure Storage all have nice solutions.