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> Implementation plan: -------------------- * Add VIR_STORAGE_TYPE_QUORUM * In src/util/virstoragefile.h change _virStorageSource to contain a virStorageSourcePtrPtr backingStores. I think doing it at this level allow to keep a 1-1 mapping with the qemu BlockDriverState hiearchy * Add a int quorum_threshold field to the same structure * Add support for parsing treshold in virDomainDiskDefParseXML * Change virDomainDiskBackingStoreParse to virDomainDiskBackingStoresParse to parse all the backingStore at once an use realloc to grow the backingStores field. * Modify virDomainDiskDefFormat to call virDomainDiskBackingStoreFormat in a loop for saving * hook into qemuBuildDriveStr around line 3442 to create the quorum parameters Do you feel that I am missing something ? Best regards Benoît