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[Qemu-devel] [Bug 568445] Re: LVM backed drives should default to cache=

From: Alex Muntada
Subject: [Qemu-devel] [Bug 568445] Re: LVM backed drives should default to cache='none'
Date: Thu, 02 Sep 2010 09:28:06 -0000

** Bug watch added: Red Hat Bugzilla #623188

** Also affects: virt-manager via
   Importance: Unknown
       Status: Unknown

LVM backed drives should default to cache='none'
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Status in QEMU: Invalid
Status in Virtual Machine Manager: Unknown
Status in “virt-manager” package in Ubuntu: Triaged

Bug description:
Binary package hint: virt-manager

KVM guests using LVM backed drives appear to experience fairly high iowait 
times on the host system if the guest has even a moderate amount of disk I/O.  
This translates to poor performance for the host and all guests running on the 
host, and appears to be due to caching as KVM defaults to using writethrough 
caching when nothing is specified.  Explicitly disabling KVM's caching appears 
to result in significantly better host and guest performance.

This is recommended in at least a few places:

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