.FP lucidasans.HTML "Venti Backups to Blu-Ray Discs".EQdelim $$.EN..TLVenti Backups to Blu-Ray Discs.AUGeoff Collyer.AI.MH.SHOverview.PPAs a precaution against multiple disks in ourPlan 9.I ventiserver's RAID array failing at about the same time,or other catastrophic failure, we record.I ventiarenas,after they are sealed,onto dual-layer Blu-Ray discs (BDs).One could use other large optical discs instead..PPThe advertised capacity of a dual-layer BD is 50GB,but those aren't even disk-manufacturer's (decimal) gigabytes,which would give a capacity of$50 times 10 sup 9$ bytes,which is roughly equivalent to 46.6 gigabytes,as the term is used by everyone but disk manufacturers.In the case of BDs,even that is an exaggeration, with the actual capacity beingcloser to $48.44 times 10 sup 9$ bytes,so the claimed capacity should be read as `50 VAX-gigabytes',where a.I VAX-gigabyteis 968,800,338 bytes.The default.I ventiarena size is 512MB, but for some reason our server is configuredwith 1GB arenas, so we could fit 46 of them on a BD.To leave a little extra room for lead-in, lead-out, inter-track gaps,lossless-linking and the like,we record 45 arenas per BD..PPThe scripts used and records kept are in.CW /sys/lib/backupand pertain to the file server on which they are stored.You will probably want to edit.CW funcsto set default file server and Blu-ray device, at minimum..SHCreating and Updating Backups.PPWe start.I cdfsafter inserting a disc (virgin or partially-written),then use.I venti/rdarenato copy the next sealed but not backed-up arenato the start of the unwritten portion of the BD by writing to.CW /mnt/cd/wd/x .We don't fixate data BDs, as that seems to tickle a bug,perhaps in our Sony Blu-Ray burners, that only records the first trackin the disc index upon fixation..PPOne can find out which arenas are sealed and which are open by viewing.CW http://\fIventi-server\fP/index .We also periodically print the most recent.I fossildump scores and save the paper with the discs..PPAll of this is packaged up as scripts in.CW /sys/lib/backup ,notably.CW backup .A typical invocation would be just.DS.ft CWcd /sys/lib/backupbackup.ft.DEwhich will guide its invoker as to which discs to insert into a Blu-rayburner and when.This works for a first full backup and for subsequent incremental backupsof just the newly-sealed arenas.There is provision for burning multiple backup sets, the default being.CW set1 .To burn a second set, we would.DS.ft CWmkdir /sys/lib/backup/set2backup -s set2.ft.DE.CW backupand related scripts keep track of which BD is current and how manytracks are recorded, and which arenas have been dumped to BD..PPWe have recorded two sets of BD backups, one of which will go toAntwerp to seed their.I ventiserver and also serve as off-site backup for Murray Hill..SHRestoring from Backups.PPAfter a disaster, or when setting up a new.I ventiserver from BD backups,the first step is to get Plan 9 running on the new.I ventiserver.This could be done by installing into a smallish (2GB).I fossilpartition from a Plan 9 installation CD, if necessary.One would then initialise the new disk partitions per.I venti-fmt (8)and read all the arenas on all the BDs into the new.I ventiby running.I venti/wrarenaonce per BD track (arena)..br.ne 3.PPTo add the contents of a backup BD to a (possibly fresh).I ventistore,shut down the.I ventiserver,format the arenas partition, thenrun.DS.ft CWrestore \fIfirst-arena-number\fP.ft.DEafter inserting a BD into the Blu-ray drive.Repeat this for each BD in the backup set.When all the arenas have been restored,it will be necessary to build a new.I ventiindex,the usual steps being to run.I checkarenas ,.I fmtisect ,.I fmtbloom ,.I fmtindex ,and.I "buildindex -b" ,all from.I venti-fmt (8).Then the.I ventiserver may be restarted..PPOnce the.I ventistorage has been restored,a new.I fossilpartition (perhaps the existing one or another one)can be initialised from the last.I fossildump score corresponding to the last arena on BD(see.I fossil/flfmtin.I fossil (4)):.DS.ft CWfossil/flfmt -v c388...32b5 /dev/sdC0/fossil.ft.DE