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https://github.com/ceph/ceph
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147 lines
2.1 KiB
ReStructuredText
147 lines
2.1 KiB
ReStructuredText
RBD Incremental Backup
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======================
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This is a simple streaming file format for representing a diff between
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two snapshots (or a snapshot and the head) of an RBD image.
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Header
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~~~~~~
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"rbd diff v1\\n"
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Metadata records
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~~~~~~~~~~~~~~~~
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Every record has a one byte "tag" that identifies the record type,
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followed by some other data.
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Metadata records come in the first part of the image. Order is not
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important, as long as all the metadata records come before the data
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records.
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From snap
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---------
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- u8: 'f'
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- le32: snap name length
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- snap name
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To snap
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-------
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- u8: 't'
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- le32: snap name length
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- snap name
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Size
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----
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- u8: 's'
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- le64: (ending) image size
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Data Records
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~~~~~~~~~~~~
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These records come in the second part of the sequence.
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Updated data
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------------
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- u8: 'w'
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- le64: offset
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- le64: length
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- length bytes of actual data
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Zero data
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---------
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- u8: 'z'
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- le64: offset
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- le64: length
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Final Record
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~~~~~~~~~~~~
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End
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---
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- u8: 'e'
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Header
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~~~~~~
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"rbd diff v2\\n"
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Metadata records
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~~~~~~~~~~~~~~~~
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Every record has a one byte "tag" that identifies the record type,
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followed by length of data, and then some other data.
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Metadata records come in the first part of the image. Order is not
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important, as long as all the metadata records come before the data
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records.
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In v2, we have the following metadata in each section:
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(1 Bytes) tag.
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(8 Bytes) length.
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(n Bytes) data.
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In this way, we can skip the unrecognized tag.
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From snap
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---------
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- u8: 'f'
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- le64: length of appending data (4 + length)
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- le32: snap name length
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- snap name
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To snap
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-------
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- u8: 't'
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- le64: length of appending data (4 + length)
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- le32: snap name length
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- snap name
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Size
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----
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- u8: 's'
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- le64: length of appending data (8)
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- le64: (ending) image size
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Data Records
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~~~~~~~~~~~~
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These records come in the second part of the sequence.
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Updated data
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------------
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- u8: 'w'
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- le64: length of appending data (8 + 8 + length)
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- le64: offset
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- le64: length
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- length bytes of actual data
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Zero data
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---------
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- u8: 'z'
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- le64: length of appending data (8 + 8)
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- le64: offset
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- le64: length
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Final Record
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~~~~~~~~~~~~
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End
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---
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- u8: 'e'
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