Re: [libvirt] Quorum block driver libvirt support proposal

The Friday 16 May 2014 à 09:54:43 (-0400), Daniel P. Berrange wrote : > On Fri, May 16, 2014 at 12:33:04PM +0200, Benoît Canet wrote: >> >> Hello list, >> >> I want to implement libvirt Quorum support. >> (https://github.com/qemu/qemu/commit/c88a1de51ab2f26a9a37ffc317249736de8c015c) >> Quorum is a QEMU RAID like block storage driver. >> Data are written on n replicas and when a read is done a comparison between the >> replica read is done. If more than threshold reads are identical the read succeed >> else it's and error. >> >> For example a Quorum with n = 3 and threshold = 2 would be made of three QCOW2 >> backing chains used as identicals replicas. threshold = 2 means that at least >> 2 replica must be identical when doing a read. >> >> I want to make use of the new backingStore xml element to implement quorum. >> >> Proposed Quorum libvirt format: >> ------------------------------- >> >> <disk type='quorum' device='disk'> >> <driver name='qemu' type='quorum'/> >> <threshold value=2/> >> <backingStore type='file'> >> <format type='qcow2'/> >> <source file='/var/lib/libvirt/images/file1.qcow2'/> >> </backingStore> >> <backingStore type='file'> >> <format type='qcow2'/> >> <source file='/var/lib/libvirt/images/file2.qcow2'/> >> </backingStore> >> <backingStore type='file'> >> <format type='qcow2'/> >> <source file='/var/lib/libvirt/images/file3.qcow2'/> >> </backingStore> >> <target dev='vda' bus='virtio'/> >> </disk> > > It feels rather odd to have <backingStore> elements but no top level > disk images. Really these are all top level images It reflect the ways QEMU does it. A single BlockDriverState holding n quorum BlockDriverState children. There is a 1-1 mapping. How would you see it ?

Best regards Benoît