Difference between revisions of "Backup"
Revision as of 16:11, 19 October 2007
If accidentally one or more files are lost from a home-directory (H:-disk) or a /vol-directory, probably the can be restored. On most C&CZ-servers every morning a "snapshot" is taken. If one contacts C&CZ system administration the same day, they can easily restore the situation of that morning with this snapshot. In other cases they have to find and read backup-tapes to restore the files. To be present on backup-tapes a file must of course be older than a few hours.
For home-PCs or other PCs that are not managed by C&CZ, the [UCI TSM taperobot] might be a good solution. Each employee can store up to 20GB on that robot without having to pay usage charges.
Different independent backup schemes are used:
- Morning snapshot to disk.
- Daily backup to tape.
- Weekly backup to tape.
- Monthly backup to tape.
- Yearly backup to tape.
Morning snapshot to disk
Many servers take a "snapshot" of their disks at 07:00 hours Monday through Friday. 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 on each H:-disk where possible a shortcut/symbolic-link ".snapshot", which makes it possible for the user to look at the snapshot himself from a Windows-PC (or any Samba client).
From a Solaris/Unix/Linx machine one can attach that H:-disk through:
or as root through:
mount -t cifs //$server/$user /$mountpoint -o user=$user
We cannot easily share the snapshot filesystem through NFS and an NFS-server does not follow 'symbolic links', that's why we have to do it as described above. The name of the shortcut/symbolic-link is chosen such that Windows shows it as a "hidden" file, in order not to confuse users. At this moment it is a pity we cannot easily have snapshots on the home-servers "grover" (KDV), "fnmrsun10" (NMR), "razor" (Research tower) and "servius" (Medical and Biophysics). Because we have snapshots, the old "Incremental backup to disk", that was hard to maintain and thought to be of less use than snapshots, was phased out.
Daily backup to tape
All server disk-partitions except temporary space like /tmp, /var/tmp, /scratch, are backed-up nightly on a few LTO2-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 latest full backups are written. These backups are started each night following a working day at 02:00 hours. The backup-tapes are preserved ca. four weeks.
Weekly, monthly and yearly backup to tape
Every weekend part of the server disk partitions are completely written to a couple of LTO2-tapes. Every partition is written to tape roughly once in four weeks. These weekly backup-tapes are preserved half a year. The monthly backup-tapes are preserved one and a half year, the yearly tapes about five years.