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Care Guide | Backups and Disaster Recovery | Backup Scheduling and Media Rotation Systems ]
Maximum Security Rotation System
This system is the "Fort Knox" of media rotation systems. It is most suitable
for computers where large quantities of data are changing all over the hard disk every
day, where the data is absolutely critical and saving a few dollars on media is
inconsequential compared to maximizing the chances of easy recovery in case of disaster.
In other words, a corporate server or large PC database being used by a number of people,
or anything that is critically important. The system also provides for a very lengthy
retention period. It requires a lot of backup media, making it only suitable for a backup
system that uses inexpensive media (generally, tape).
This system is based on a scheme I developed for the minicomputer I manage at my
office. I don't really recommend this type of system for the average home user, since it
is probably overkill based on what most people use their PCs for, and is expensive.
However, if you want the ultimate in backup protection, this is it.
Here's how the system works:
- Backup Method and Type: Backups are performed on an 8mm tape backup unit. All
backups are full backups, no incrementals are needed since the full backup will fit on one
tape and only takes about two hours to do the whole system.
- Media Set Groupings: The system uses two different groups of media sets. The
first group is for rotational daily backups, the second for permanent monthly and yearly
backups. The number of tapes used depends on the retention period wanted. I use 10 daily
backup tapes, 22 monthly tapes and 5 yearly tapes. This allows me to see a daily snapshot
going back about 2 weeks (we back up 5 days a week since the office is normally closed on
the weekend), a monthly snapshot going back 2 years, and an annual snapshot going back 5
years. The total media requirement is 37 tapes. If your system is used 7 days per week,
then the number of daily tapes may need to be increased.
- Rotational Daily Backups: On days other than month-end, daily backups are done
using one of the daily rotation tapes; first tape #1, then tape #2 etc., until tape #10 is
reached, then returning to tape #1. Tape #10 is normally stored off-site so that about
every two weeks the off-site backup is refreshed.
- Monthly Backups: On the month-end date the daily rotation is skipped for one day
and a permanent backup tape is used. If the month-end date is also year-end, then a
year-end tape is used, otherwise, a monthly tape is selected. In both cases, the oldest
permanent backup is "recycled". So for year-end 1998, the tape that had year-end
1993 is recycled. Similarly, the oldest monthly backup is recycled and used for the
current monthly backup.
Tip: Some companies might not
want to recycle year-end tapes at all. It's a small price to pay (a few dollars a year) to
keep a permanent record of all year-end backups, just in case. Do bear in mind that the shelf life of magnetic media is limited, however, so
don't expect the tapes to still work after say, 20 years.
- Backup Logging: A log is kept near the tape drive, and on it is recorded the date
of each backup and which tape was used. Each tape has the date recorded on it when it is
- Drive Cleaning: The tape drive head is cleaned weekly using a cleaning tape
specifically designed for it.
- Media Storage: All backup tapes are stored in a fire-proof, locked safe, on the
premises. One of the daily backup tapes is stored off-site at all times.
- Media Replacement: All of the daily rotation tapes are replaced once every
two years, to greatly reduce the chance of media wearout. These are the tapes that are
used most often, and after two years each tape will have been used about 50 times.
This system provides the following advantages:
- Resistance to Media Failure: There is virtually no chance of a great deal of data
being lost, due to the number of tapes used in the system. Since incrementals backups are
not being used, there is a great deal of data redundancy on the backup tapes. The tapes
that are heavily used are replaced regularly to avoid the chance of wearout.
- Excellent Retention Period: I can go back and see the state of the data files as
they existed at month-end for the past two years, and at year-end for the last five years
- Rapid Restoration: Since incremental backups are not used, a restore in the event
of a problem will be much more rapid since it can be done from one tape.
- Disaster Protection: A safe is used for storing media. Since tapes are rotated
off-site, there is increased protection against total loss of the building.
Next: Scheduling Considerations for Multiple PCs
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