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  1. .HTML "Venti Backups to Blu-Ray Discs"
  2. .EQ
  3. delim $$
  4. .EN
  5. .
  6. .TL
  7. Venti Backups to Blu-Ray Discs
  8. .AU
  9. Geoff Collyer
  10. .AI
  11. .MH
  12. .SH
  13. Overview
  14. .PP
  15. As a precaution against multiple disks in our
  16. Plan 9
  17. .I venti
  18. server's RAID array failing at about the same time,
  19. or other catastrophic failure, we record
  20. .I venti
  21. arenas,
  22. after they are sealed,
  23. onto dual-layer Blu-Ray discs (BDs).
  24. One could use other large optical discs instead.
  25. .PP
  26. The advertised capacity of a dual-layer BD is 50GB,
  27. but those aren't even disk-manufacturer's (decimal) gigabytes,
  28. which would give a capacity of
  29. $50 times 10 sup 9$ bytes,
  30. which is roughly equivalent to 46.6 gigabytes,
  31. as the term is used by everyone but disk manufacturers.
  32. In the case of BDs,
  33. even that is an exaggeration, with the actual capacity being
  34. closer to $48.44 times 10 sup 9$ bytes,
  35. so the claimed capacity should be read as `50 BD-gigabytes',
  36. where a
  37. .I BD-gigabyte
  38. is 968,800,338 bytes.
  39. The default
  40. .I venti
  41. arena size is 512MB, but for some reason our server is configured
  42. with 1GB arenas, so we could fit 46 of them on a BD.
  43. To leave a little extra room for lead-in, lead-out, inter-track gaps,
  44. lossless-linking and the like,
  45. we record 45 arenas per BD.
  46. .PP
  47. The scripts used and records kept are in
  48. .CW /sys/lib/backup
  49. and pertain to the file server on which they are stored.
  50. You will probably want to edit
  51. .CW funcs
  52. to set default file server and Blu-ray device, at minimum.
  53. .SH
  54. Creating and Updating Backups
  55. .PP
  56. We start
  57. .I cdfs
  58. after inserting a disc (virgin or partially-written),
  59. then use
  60. .I venti/rdarena
  61. to copy the next sealed but not backed-up arena
  62. to the start of the unwritten portion of the BD by writing to
  63. .CW /mnt/cd/wd/x .
  64. We don't fixate data BDs, as that seems to tickle a bug,
  65. perhaps in our Sony Blu-Ray burners, that only records the first track
  66. in the disc index upon fixation.
  67. .PP
  68. One can find out which arenas are sealed and which are open by viewing
  69. .CW http://\fIventi-server\fP/index .
  70. We also periodically print the most recent
  71. .I fossil
  72. dump scores and save the paper with the discs.
  73. .PP
  74. All of this is packaged up as scripts in
  75. .CW /sys/lib/backup ,
  76. notably
  77. .CW backup .
  78. A typical invocation would be just
  79. .DS
  80. .ft CW
  81. cd /sys/lib/backup
  82. backup
  83. .ft
  84. .DE
  85. which will guide its invoker as to which discs to insert into a Blu-ray
  86. burner and when.
  87. This works for a first full backup and for subsequent incremental backups
  88. of just the newly-sealed arenas.
  89. There is provision for burning multiple backup sets, the default being
  90. .CW set1 .
  91. To burn a second set, we would
  92. .DS
  93. .ft CW
  94. mkdir /sys/lib/backup/set2
  95. backup -s set2
  96. .ft
  97. .DE
  98. .CW backup
  99. and related scripts keep track of which BD is current and how many
  100. tracks are recorded, and which arenas have been dumped to BD.
  101. .PP
  102. We have recorded two sets of BD backups, one of which will go to
  103. Antwerp to seed their
  104. .I venti
  105. server and also serve as off-site backup for Murray Hill.
  106. .SH
  107. Restoring from Backups
  108. .PP
  109. After a disaster, or when setting up a new
  110. .I venti
  111. server from BD backups,
  112. the first step is to get Plan 9 running on the new
  113. .I venti
  114. server.
  115. This could be done by installing into a smallish (2GB)
  116. .I fossil
  117. partition from a Plan 9 installation CD, if necessary.
  118. One would then initialise the new disk partitions per
  119. .I venti-fmt (8)
  120. and read all the arenas on all the BDs into the new
  121. .I venti
  122. by running
  123. .I venti/wrarena
  124. once per BD track (arena).
  125. .br
  126. .ne 3
  127. .PP
  128. To add the contents of a backup BD to a (possibly fresh)
  129. .I venti
  130. store,
  131. shut down the
  132. .I venti
  133. server,
  134. format the arenas partition, then
  135. run
  136. .DS
  137. .ft CW
  138. restore \fIfirst-arena-number\fP
  139. .ft
  140. .DE
  141. after inserting a BD into the Blu-ray drive.
  142. Repeat this for each BD in the backup set.
  143. When all the arenas have been restored,
  144. it will be necessary to build a new
  145. .I venti
  146. index,
  147. the usual steps being to run
  148. .I checkarenas ,
  149. .I fmtisect ,
  150. .I fmtbloom ,
  151. .I fmtindex ,
  152. and
  153. .I "buildindex -b" ,
  154. all from
  155. .I venti-fmt (8).
  156. Then the
  157. .I venti
  158. server may be restarted.
  159. .PP
  160. Once the
  161. .I venti
  162. storage has been restored,
  163. a new
  164. .I fossil
  165. partition (perhaps the existing one or another one)
  166. can be initialised from the last
  167. .I fossil
  168. dump score corresponding to the last arena on BD
  169. (see
  170. .I fossil/flfmt
  171. in
  172. .I fossil (4)):
  173. .DS
  174. .ft CW
  175. fossil/flfmt -v c388...32b5 /dev/sdC0/fossil
  176. .ft
  177. .DE