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Hi,
We are currently testing the performance with rbd caching enabled with write-back mode on our openstack (grizzly) nova nodes. By default, nova fires up the rbd volumes with "if=none" mode evidenced by the following cmd line from "ps | grep". -drive file=rbd:ceph-openstack-volumes/volume-949e2e32-20c7-45cf-b41b-46951c78708b:id=ceph-openstack-volumes:key=12347I9RsEoIDBAAi2t+M6+7zMMZoMM+aasiog==:auth_supported=cephx\;none,if=none,id=drive-virtio-disk0,format=raw,serial=949e2e32-20c7-45cf-b41b-46951c78708b,cache=writeback Does anyone know if this should be set to anything else (e.g., if=virtio suggested by some qemu posts in general)? Given that the underline network stack for RBD IO is provided by the linux kenerl instead, does this option bear any relevance for rbd volume performance inside guest VM? Thanks. --weiguo |
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