qemu/docs/block-replication.txt

11 for COLO (COarse-grain LOck-stepping) where the Secondary VM is running.
13 where the Secondary VM is not running.
19 consecutive checkpoints. The VM state of the Primary and Secondary VM is
22 the modified disk contents in the Secondary VM must be buffered, and are
25 the Primary disk are asynchronously forwarded to the Secondary node.
31         |Primary Write Requests|            |Secondary Write Requests|
46            | Primary Disk |           | Secondary Disk |
49     1) Primary write requests will be copied and forwarded to Secondary
51     2) Before Primary write requests are written to Secondary disk, the
52        original sector content will be read from Secondary disk and
54        sector content (it could be from either "Secondary Write Requests" or
56     3) Primary write requests will be written to Secondary disk.
57     4) Secondary write requests will be buffered in the Disk buffer and it
66              |            ||                            | Secondary
77 Primary |                 ||  Secondary disk <--------- hidden-disk 5 <--------- active-disk 4
86 runs the secondary VM. The read pattern (fifo) for quorum can be extended
93 3) The secondary disk receives writes from the primary VM through QEMU's
96 4) The disk on the secondary is represented by a custom block device
106 of the NBD server into the secondary disk. So before block replication,
107 the primary disk and secondary disk should contain the same data.
109 7) The secondary also has a quorum node, so after secondary failover it
118 4. I/O error on secondary disk
126 in Secondary's write operation (what decides which target to write).
132    We must call block_replication_start_all() in secondary QEMU before
138    Secondary QEMU. The Disk buffer will be dropped in this interface.
147    Secondary Disk and stop block replication. The vm should be stopped
172   2. host is the secondary physical machine's hostname or IP
177      secondary qemu.
180 Secondary:
182   -drive if=none,id=childs1,driver=replication,mode=secondary,top-id=top-disk1
191   Then run qmp command in secondary qemu:
211   1. The export name in secondary QEMU command line is the secondary
224   The secondary host is down, so we should run the following qmp command
239 Secondary:
243 Promote Secondary to Primary: