[ubuntu-cloud] Ubuntu on Azure

[John Kew]

Hey Folks;

We are seeing some rather unique issues on the Azure environment with
Ubuntu. There is intermittent blocking io on the OS Disk > 120 seconds;
resulting in a kernel stack trace. We have also seen the RCU stall timeout
occur. This occurs on multiple vms; but it often occurs in groups among two
or more VMs. The issue occurs once or twice per day on a cluster of about
60 VMs.

We have certainly isolated many of the host issues;  storage account
issues, etc, with Microsoft but I wanted to get a better understanding on
the changes required to support Ubuntu on Azure.

Beyond the hyper-v driver and waagent; are there any unique kernel settings
required on these VMs? Where any modifications to the hyper-v drivers
required to support Azure?

I'm trying to digest the problem more throughly from the engineering side
so I can make headway on this.

-John
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