dear list, 

I recently had a machine lose power that was unfortunately running between 
15-20 kvm guests. 

The server is a Dell R710 with an H700 controller with 1gb of nvcache. 
Writeback cache is enabled on the controller. There is a mix of linux and 
windows guests, some with qcow2 format vdisks and others with raw format 
vdisks. Some of these guests have wb cache enabled on the vdisks and some do 
not. 

About a third of the guests experienced disk corruption after coming back up 
after the host lost power. Based on what I have read, this should not have 
happened using the above configuration. The operating system is Centos 6.2, 
this is all direct attached storage configured as raid 1 mirrors. 

I'm hoping someone has a comment or suggestion on this so that I can take 
action to prevent corruption in the future. 

The motivation to enable write caching is primarily performance. 

Thanks, 

Ron 
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