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This bug has been copied from Engineeringbug #653536 and has been proposed to be backported to 6.0 z-stream (EUS).
For qemu-kvm-0.12.1.2-2.113.el6_0.4: # time strace -o 113_4.log qemu-img convert -f qcow2 /mnt/rhel39-32.qcow2 -O qcow2 /mnt/113_4.qcow2 real 5m8.992s user 0m21.775s sys 1m8.603s # grep fdatasync 113_4.log |wc -l 101689 For qemu-kvm-0.12.1.2-2.113.el6_0.5: # time strace -o 113_5.log qemu-img convert -f qcow2 /mnt/rhel39-32.qcow2 -O qcow2 /mnt/113_5.qcow2 real 2m10.605s user 0m18.323s sys 0m41.449s # grep fdatasync 113_5.log |wc -l 0 # /usr/libexec/qemu-kvm --help |grep cache [,cache=writethrough|writeback|none|unsafe][,format=f] Based on the above, this bug is fixed.
Technical note added. If any revisions are required, please edit the "Technical Notes" field accordingly. All revisions will be proofread by the Engineering Content Services team. New Contents: Previously, the conversion of a disk image by using the "qemu-img convert" command may have been significantly slow. With this update, various patches have been applied to improve the performance of the above command.
An advisory has been issued which should help the problem described in this bug report. This report is therefore being closed with a resolution of ERRATA. For more information on therefore solution and/or where to find the updated files, please follow the link below. You may reopen this bug report if the solution does not work for you. http://rhn.redhat.com/errata/RHBA-2011-0012.html