- Your files are everything! Their contents must be
preserved lest your system be useless.
- Backup (the act of copying files to a secondary medium to
insure their contents are not lost) is a critical task.
Backup tapes are as valuable as the files they contain and
must have the same security precautions employed in their
handling as did the original files.
- Everyone has a backup strategy, whether they know it or not.
It's best to have a good one.
- Backup and Restore are critical activities that users
tend to take for granted. This is one area that we've ignored
on our systems, but that cannot be ignored in practice.
- I'm reminded of a situation in which a group was going to take
control of a delegated subnet (to increase their perceived
level of service). When asked what their backup strategy would
be, the soon to be administrator shrugged his shoulders and
said, ''We'll throw in a tape.''
This is not an example of a robust backup strategy.
- Answer these questions:
- What files need to be backed up?
- On what filesystems/devices do they reside?
- When/where/how should backups be performed?
- How often do file contents change and how recent
should the backup be?
- How quickly and by whom should damaged/deleted files
be restored?
- Where (into what directories) will files be restored?
- Backups can backup the full filesystem or only the
incremental changes since a previous backup.
- Unix dump/restore and numerous other backup systems employ
a hierarchy of full and incremental backups with level
numbers. We present the dump/restore level number convention
here.
A level 0 backup is a full backup.
A level n backup (where n > 0) is a backup of
all files that have changed since the most recent backup at
a level less than n.
- Increments are used so that backup creation can run faster
since fewer files need to be copied.
This has the negative
effect that a restore of a single file may require each
level tape to be read (if the file is only on the level 0
tape). And a full system restore will certainly
require each level's tape to be read.
Unix dump does not keep track of deleted files. What consequence
does this lead to in the case of a full system restore.
- One old CISE Department plan was this:
Once per semester: Level 0 backup
Once per month: Level 1 backup
Once per week: Level 6 backup
Once per night: Level 9 backup
- Backups can be carried out either attended (with an
administrator present) or unattended. Unattended
backups require that the appropriate media will be in place
in the backup device when backup starts. This means
the backup device must be physically secure.
- Storing backup media is critical for the following reasons:
- Each administrator needs to know where the backup
media are and how they are catalogued.
- Media should be stored in a place that makes
restorations easy and timely.
- Backup media should be write protected.
- Backup media must be stored in a friendly environment
(low humidity, cool).
- Backup media must be handled as little as possible
- Backup media must be stored in as secure a location
as the original files.
- Off-site storage should be such that if the system
administrators could have survived a disaster but the systems
did not, the entire system can be reconstructed.
Could you survive a nuclear bomb hit at your workplace.