CERN backup setup ca. 2011

Base numbers

backup dumps: daily
backup retention policy: 6 months
restore directly done by the users (that is w/o admin intervention)
same backup policy for all volumes: all volumes are equal and no volumes are more equal than others

components:
- frontend: AFS "native" backup system (butc, backup commands)
- tape backend: TSM backup service and tape manager
granularity:
- full backup cycle to tape ~ every 30-50 days
- 1 or 2 differential backups to tape per full backup cycle (differential = "diff to the last full")
- daily incremental backups to tape ("diff to the last incremental")
- "yesterday" also available as “BK” clone on disk
  - for home directories these clones are already mounted and directly accessible to users
servers are backed-up in parallel by a cronjob every evening (i.e. every 24 hours)
- partitions on a server are backup-up in sequence
load-balancing the data flow to the backup service:
- avoid all servers doing full backups at the same time

scalability: need 24 hour window to complete a dump of all partitions on a server (may be a problem for increasingly larger servers)
- more parallelism in dumping the volumes?
- using more features of the TSM (e.g. more accounts) may be required in the future
maintenance:
- current administration layer for backup dump/restore is overly complex and drags a lot of historical/obsolete code

AFS backup system frontend
- backup volsets: one volset per partition
  - database model: a volset dump contains a list of volume dumps
- dump hierarchy:
  - simply defined as a chain: full-i1-...-i52 (no differentials)
  - differential backups are determined based on additional state information stored locally via perl Catalog module
  - once a differential is created, the backup database keeps track of the parentship of subsequent incrementals
- several layers of wrappers perl/ksh/arc/... to manage dumps and restores
  - butc wrapped by expect script and fired on demand (no permanent butc processes), requires locking
  - end-user backup restore integrated into the afs_admin interface
    - restore done in a “synchronous” mode: an authenticated RPC to a restore server (one of afs file server nodes) is made using "arc"
    - the RPC connection is kept alive until user leaves a temporary shell which is positioned where recovered volumes are temporarily mounted
TSM backend
- TSM server (one TSM account at the moment, using "archive" mode)
- butc linked against XBSA/TSM library
  - each volume dump is stored as a separate object in TSM with the volset dump id prefix ("/{volsetdumpid}/{volname}.backup")