Backup Policy

TIG managed AFS and NFS storage space is backed up on the following schedule

• Full backups (level 0)
  • Taken Quarterly
  • Archived permanently (1st year off site)
• Monthly backups (level 1)
  • Taken monthly (of course)
  • Mirrored tape writes
  • One copy stored offsite for one year
  • Archived permanently
• Weekly backups (level 2)
  • Taken weekly (of course)
  • Archived for one month
• Daily backups (incremental)
  • Taken daily
  • Archived for two weeks

Additionally AFS storage is snapshotted nightly. A copy-on-write snapshot of each volume is available, however only the AFS home directory has the snapshot mounted by default (as ~/.snapshot). If you need the snapshot feature and your AFS project directory or AFS group directory does not have a .snapshot subdirectory please email help@csail.mit.edu and we can set this up for you.

As can be seen from this schedule, the monthly backup is the only level of granularity guaranteed over time. For requests of data less that two weeks old we can usually provide single-day resolution. Between two and four weeks, we can only resolve to the week level. Past that it's monthly.

The some what odd four level backup system with mirrored level one backups allows us to conserve tape since we only write out full data once per year and the monthlies tend to be about 20% this size. The mirrored monthlies allow us to lose any one tape without losing data. A lost full can be reconstructed from previous monthly and full tapes, and there are two copies of each monthly.

-- JonProulx - 28 Dec 2004