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