If accidentally one or more files are lost from a home-directory (H:-disk) or a /vol-directory, probably the files can be restored. On most C&CZ-servers every morning a "snapshot" is taken, on some servers even a few times each day. If one contacts C&CZ system administration the same day, most of the time we can easily restore the situation of that morning with this snapshot. In other cases we have to revert to the backup-tapes to restore the files. To be present on backup-tapes a file must of course have existed during a (nightly) backup.
Different independent backup schemes are used:
- Morning snapshots to disk.
- Daily backups to tape.
- Monthly backups to tape.
- Yearly backups to tape.
Morning snapshots to disk
A few servers take a "snapshot" of their disks at 07:00 hours Monday through Friday, and on some Linux servers at 13:00 hours as well. With this snapshot C&CZ system administration can see the exact situation of that morning, which makes an "undelete" easy. If a user wants to be able to do this himself, C&CZ can create a network share, which makes it possible for the user to look at the snapshot himself from a Windows-PC (or any Samba client).
From a Unix/Linux machine one can attach that network share through:
or as root through:
mount -t cifs //$server/$sharename /$mountpoint -o user=$user
The regular servers for the home-directories of students and staff are bundle and pile.
We cannot easily share the snapshot filesystem through NFS and an NFS- or CIFS/SMB-server does not follow 'symbolic links', that's why we have to do it as described above.
Daily backup to tape
All server disk-partitions except temporary space like /tmp, /var/tmp, /scratch, are backed-up after each working day on a number of tapes. Because of the time it takes to do a backup, most of the times this is a so-called incremental dump, which means that only changes w.r.t. the previous backup are written. These backups are started each evening after 18:00 hours. These backup-tapes are preserved for four weeks.
Monthly and yearly backup to tape
Every weekend a subset of all server disk partitions are completely written to a couple of LTO6-tapes. Every partition is written to tape roughly once every four weeks. These monthly backup-tapes are preserved for one year. The yearly backups are performed around the Chrismas break (end of December and start of January) and are preserved for at least five years.
The backups are made with the Amanda open source network backup software. The backup server, that was renewed in 2013, is a Dell PowerEdge R720xd with 44 TB disc space, that is used to make fast restores from disk possible. The backups are written to LTO-6 tapes in a Dell TL2000 tape library with 2 LTO6 drives and 24 slots. The new service reads and writes LTO-6, but it can also read the LTO-4 tapes that we used before.
The full backup schedule (Daily plus Monthly plus Yearly backups) costs 375 €/TB year. It breaks down to:
- Daily: 175 €/TB year
- Monthly: 140 €/TB year
- Yearly: 60 €/TB year
The costs of backup are the major part of the cost of C&CZ disc space.