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author | Marcelo Tosatti <mtosatti@redhat.com> | 2012-01-18 14:40:54 +0000 |
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committer | Kevin Wolf <kwolf@redhat.com> | 2012-01-26 14:49:18 +0100 |
commit | 094f1ba10ab341b8d1306e863698a07b2afa6b09 (patch) | |
tree | 9cf8a2ddb06c63cf1e78fe7a7749a56361a462b3 /docs | |
parent | c8c3080f4a6fbbf3c9c5d6efd1b49e7ca6479d1e (diff) | |
download | hqemu-094f1ba10ab341b8d1306e863698a07b2afa6b09.zip hqemu-094f1ba10ab341b8d1306e863698a07b2afa6b09.tar.gz |
docs: describe live block operations
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Diffstat (limited to 'docs')
-rw-r--r-- | docs/live-block-ops.txt | 58 |
1 files changed, 58 insertions, 0 deletions
diff --git a/docs/live-block-ops.txt b/docs/live-block-ops.txt new file mode 100644 index 0000000..a257087 --- /dev/null +++ b/docs/live-block-ops.txt @@ -0,0 +1,58 @@ +LIVE BLOCK OPERATIONS +===================== + +High level description of live block operations. Note these are not +supported for use with the raw format at the moment. + +Snapshot live merge +=================== + +Given a snapshot chain, described in this document in the following +format: + +[A] -> [B] -> [C] -> [D] + +Where the rightmost object ([D] in the example) described is the current +image which the guest OS has write access to. To the left of it is its base +image, and so on accordingly until the leftmost image, which has no +base. + +The snapshot live merge operation transforms such a chain into a +smaller one with fewer elements, such as this transformation relative +to the first example: + +[A] -> [D] + +Currently only forward merge with target being the active image is +supported, that is, data copy is performed in the right direction with +destination being the rightmost image. + +The operation is implemented in QEMU through image streaming facilities. + +The basic idea is to execute 'block_stream virtio0' while the guest is +running. Progress can be monitored using 'info block-jobs'. When the +streaming operation completes it raises a QMP event. 'block_stream' +copies data from the backing file(s) into the active image. When finished, +it adjusts the backing file pointer. + +The 'base' parameter specifies an image which data need not be streamed from. +This image will be used as the backing file for the active image when the +operation is finished. + +In the example above, the command would be: + +(qemu) block_stream virtio0 A + + +Live block copy +=============== + +To copy an in use image to another destination in the filesystem, one +should create a live snapshot in the desired destination, then stream +into that image. Example: + +(qemu) snapshot_blkdev ide0-hd0 /new-path/disk.img qcow2 + +(qemu) block_stream ide0-hd0 + + |