ceph/doc/dev/rbd-export.rst

   1 RBD Export & Import
   2 ===================
   3
   4 This is a file format of an RBD image or snapshot. It's a sparse format
   5 for the full image. There are three recording sections in the file.
   6
   7 (1) Header.
   8 (2) Metadata.
   9 (3) Diffs.
  10
  11 Header
  12 ~~~~~~
  13
  14 "rbd image v2\\n"
  15
  16 Metadata records
  17 ~~~~~~~~~~~~~~~~
  18
  19 Every record has a one byte "tag" that identifies the record type,
  20 followed by length of data, and then some other data.
  21
  22 Metadata records come in the first part of the image.  Order is not
  23 important, as long as all the metadata records come before the data
  24 records.
  25
  26 In v2, we have the following metadata in each section:
  27 (1 Bytes) tag.
  28 (8 Bytes) length.
  29 (n Bytes) data.
  30
  31 In this way, we can skip the unrecognized tag.
  32
  33 Image order
  34 -----------
  35
  36 - u8: 'O'
  37 - le64: length of appending data (8)
  38 - le64: image order
  39
  40 Image format
  41 ------------
  42
  43 - u8: 'F'
  44 - le64: length of appending data (8)
  45 - le64: image format
  46
  47 Image Features
  48 --------------
  49
  50 - u8: 'T'
  51 - le64: length of appending data (8)
  52 - le64: image features
  53
  54 Image Stripe unit
  55 -----------------
  56
  57 - u8: 'U'
  58 - le64: length of appending data (8)
  59 - le64: image striping unit
  60
  61 Image Stripe count
  62 ------------------
  63
  64 - u8: 'C'
  65 - le64: length of appending data (8)
  66 - le64: image striping count
  67
  68 ImageMeta Key and Value
  69 -----------------------
  70
  71 - u8: 'M'
  72 - le64: length of appending data (length of key + length of value + 4 * 2)
  73 - string: image-meta key
  74 - string: image-meta value
  75
  76 Final Record
  77 ~~~~~~~~~~~~
  78
  79 End
  80 ---
  81
  82 - u8: 'E'
  83
  84
  85 Diffs records
  86 ~~~~~~~~~~~~~
  87
  88 Record the all snapshots and the HEAD in this section.
  89
  90 Snap Protection status
  91 ----------------------
  92
  93 Record the snapshot's protection status if `--export-format=2`.
  94 - u8: 'p'
  95 - le64: length of appending data (8)
  96 - u8: snap protection status (0 for false, 1 for true)
  97
  98 Others
  99 ------
 100
 101 - le64: number of diffs
 102 - Diffs ...
 103
 104 Detail please refer to rbd-diff.rst