Casey Bralla on 21 Sep 2010 15:05:04 -0700

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[PLUG] Need Troubleshooting Advice: Disk Errors in Virtual Machines

I've got a weird problem which I hope somebody here can help me figure out.

I'm running about a dozen virtual machines (mostly web servers) on a triple-
core AMD system running Debian Lenny (ie: "Stable").  Each of the virtual 
machines is also running Debian Lenny.

I am having repeated disk errors on the Virtual Machines, but no disk errors 
on the host machine.  These disk errors often cause a Kernel Panic within the 
VM, or otherwise crash the web server on the VM.

There appears to be no overall pattern to the crashes.  It can happen after an 
hour, or a week.  It can happen in any of the Virtual Machines.  However, I 
have noticed that it often happens in several (2 or 3) VMs at the same time.

I haven't found anything in the logs (yet) to identify a culprit.

I've tried using both IDE and SATA disk interfaces to the virtual disks.  I've 
tried running both VirtualBox and VMware Server.  I've mucked around with 
several BIOS setting related to Disk I/O and virtualization.

I've run Memtest86 (but just for a half-hour) and found no memory errors.  My 
disk SMART interface records no errors with the physical disk.

The host machine is somewhat RAM-constrained, but does not appear to be 
unreasonably so.  The CPUs do not seem to be overly loaded, although I suspect 
that the problem occurs when one of the VMs gets taxed.  (No real data for 
this, however... just a hunch.)

Anybody have any thoughts on what might cause these disk errors, or what I 
might check?


Casey Bralla
Chief Nerd in Residence
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