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58 lines
1.8 KiB
Text
58 lines
1.8 KiB
Text
LIVE BLOCK OPERATIONS
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=====================
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High level description of live block operations. Note these are not
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supported for use with the raw format at the moment.
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Snapshot live merge
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===================
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Given a snapshot chain, described in this document in the following
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format:
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[A] -> [B] -> [C] -> [D]
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Where the rightmost object ([D] in the example) described is the current
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image which the guest OS has write access to. To the left of it is its base
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image, and so on accordingly until the leftmost image, which has no
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base.
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The snapshot live merge operation transforms such a chain into a
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smaller one with fewer elements, such as this transformation relative
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to the first example:
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[A] -> [D]
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Currently only forward merge with target being the active image is
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supported, that is, data copy is performed in the right direction with
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destination being the rightmost image.
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The operation is implemented in QEMU through image streaming facilities.
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The basic idea is to execute 'block_stream virtio0' while the guest is
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running. Progress can be monitored using 'info block-jobs'. When the
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streaming operation completes it raises a QMP event. 'block_stream'
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copies data from the backing file(s) into the active image. When finished,
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it adjusts the backing file pointer.
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The 'base' parameter specifies an image which data need not be streamed from.
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This image will be used as the backing file for the active image when the
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operation is finished.
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In the example above, the command would be:
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(qemu) block_stream virtio0 A
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Live block copy
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===============
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To copy an in use image to another destination in the filesystem, one
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should create a live snapshot in the desired destination, then stream
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into that image. Example:
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(qemu) snapshot_blkdev ide0-hd0 /new-path/disk.img qcow2
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(qemu) block_stream ide0-hd0
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