From 2b5e1aa4d0644977dacbcd9e45ca92a7e5626851 Mon Sep 17 00:00:00 2001 From: Jeffrey Cody Date: Wed, 21 Mar 2012 21:55:15 +0100 Subject: [PATCH 48/55] docs: describe live block operations RH-Author: Jeffrey Cody Message-id: <281785726529a6158a1f2e66355ceffe15065a21.1332362400.git.jcody@redhat.com> Patchwork-id: 38897 O-Subject: [RHEL6.3 qemu-kvm PATCH v8 48/54] docs: describe live block operations Bugzilla: 582475 RH-Acked-by: Paolo Bonzini RH-Acked-by: Marcelo Tosatti RH-Acked-by: Kevin Wolf From: Marcelo Tosatti Signed-off-by: Marcelo Tosatti Signed-off-by: Stefan Hajnoczi Signed-off-by: Kevin Wolf (cherry picked from commit 094f1ba10ab341b8d1306e863698a07b2afa6b09) Signed-off-by: Stefan Hajnoczi Signed-off-by: Anthony Liguori Signed-off-by: Jeff Cody --- docs/live-block-ops.txt | 58 +++++++++++++++++++++++++++++++++++++++++++++++ 1 files changed, 58 insertions(+), 0 deletions(-) create mode 100644 docs/live-block-ops.txt Signed-off-by: Michal Novotny --- docs/live-block-ops.txt | 58 +++++++++++++++++++++++++++++++++++++++++++++++ 1 files changed, 58 insertions(+), 0 deletions(-) create mode 100644 docs/live-block-ops.txt 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 + + -- 1.7.7.6