2 .HTML "Venti Backups to Blu-Ray Discs"
8 Venti Backups to Blu-Ray Discs
16 As a precaution against multiple disks in our
19 server's RAID array failing at about the same time,
20 or other catastrophic failure, we record
23 after they are sealed,
24 onto dual-layer Blu-Ray discs (BDs).
25 One could use other large optical discs instead.
27 The advertised capacity of a dual-layer BD is 50GB,
28 but those aren't even disk-manufacturer's (decimal) gigabytes,
29 which would give a capacity of
30 $50 times 10 sup 9$ bytes,
31 which is roughly equivalent to 46.6 gigabytes,
32 as the term is used by everyone but disk manufacturers.
34 even that is an exaggeration, with the actual capacity being
35 closer to $48.44 times 10 sup 9$ bytes,
36 so the claimed capacity should be read as `50 VAX-gigabytes',
42 arena size is 512MB, but for some reason our server is configured
43 with 1GB arenas, so we could fit 46 of them on a BD.
44 To leave a little extra room for lead-in, lead-out, inter-track gaps,
45 lossless-linking and the like,
46 we record 45 arenas per BD.
48 The scripts used and records kept are in
50 and pertain to the file server on which they are stored.
51 You will probably want to edit
53 to set default file server and Blu-ray device, at minimum.
55 Creating and Updating Backups
59 after inserting a disc (virgin or partially-written),
62 to copy the next sealed but not backed-up arena
63 to the start of the unwritten portion of the BD by writing to
65 We don't fixate data BDs, as that seems to tickle a bug,
66 perhaps in our Sony Blu-Ray burners, that only records the first track
67 in the disc index upon fixation.
69 One can find out which arenas are sealed and which are open by viewing
70 .CW http://\fIventi-server\fP/index .
71 We also periodically print the most recent
73 dump scores and save the paper with the discs.
75 All of this is packaged up as scripts in
79 A typical invocation would be just
86 which will guide its invoker as to which discs to insert into a Blu-ray
88 This works for a first full backup and for subsequent incremental backups
89 of just the newly-sealed arenas.
90 There is provision for burning multiple backup sets, the default being
92 To burn a second set, we would
95 mkdir /sys/lib/backup/set2
100 and related scripts keep track of which BD is current and how many
101 tracks are recorded, and which arenas have been dumped to BD.
103 We have recorded two sets of BD backups, one of which will go to
104 Antwerp to seed their
106 server and also serve as off-site backup for Murray Hill.
108 Restoring from Backups
110 After a disaster, or when setting up a new
112 server from BD backups,
113 the first step is to get Plan 9 running on the new
116 This could be done by installing into a smallish (2GB)
118 partition from a Plan 9 installation CD, if necessary.
119 One would then initialise the new disk partitions per
121 and read all the arenas on all the BDs into the new
125 once per BD track (arena).
129 To add the contents of a backup BD to a (possibly fresh)
135 format the arenas partition, then
139 restore \fIfirst-arena-number\fP
142 after inserting a BD into the Blu-ray drive.
143 Repeat this for each BD in the backup set.
144 When all the arenas have been restored,
145 it will be necessary to build a new
148 the usual steps being to run
159 server may be restarted.
163 storage has been restored,
166 partition (perhaps the existing one or another one)
167 can be initialised from the last
169 dump score corresponding to the last arena on BD
176 fossil/flfmt -v c388...32b5 /dev/sdC0/fossil