Bug 710145

Summary:	RFE: qcow2 performance, preallocation vs dynamic
Product:	[Community] Virtualization Tools	Reporter:	Gary Scarborough <gscarborough>
Component:	virt-manager	Assignee:	Cole Robinson <crobinso>
Status:	CLOSED UPSTREAM	QA Contact:
Severity:	unspecified	Docs Contact:
Priority:	unspecified
Version:	unspecified	CC:	berrange, crobinso, xen-maint
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Hardware:	Unspecified
OS:	Linux
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Fixed In Version:		Doc Type:	Bug Fix
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Clone Of:		Environment:
Last Closed:	2013-10-01 18:54:58 UTC	Type:	---
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
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oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:

Description Gary Scarborough 2011-06-02 14:25:41 UTC

Description of problem:

As seen in this article, 

http://www.ilsistemista.net/index.php/virtualization/11-kvm-io-slowness-on-rhel-6.html

which has been mentioned in other bug reports, qcow2 suffers from performance problems depending on both caching and preallocation.  Raw however, has almost no difference in speed between preallocated and dynamic disk files.  Is this a function of qcow2 or something that can be fixed?  It is really convenient being able to assign a system 100 GB of space but only having to back up what is actually being used.  But the performance hit when using qcow2 is substantial.  Can this be corrected?

Comment 1 Cole Robinson 2013-10-01 18:54:58 UTC

Upstream we now do qcow2 preallocation by default for all qcow2 creation, if libvirt supports it