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8 Backups.

8.1 Media types

Here are some average example prices as of February 1998:

Table 4: Backup media comparison 
Type         Drive price  Media price  Capacity   Price/MB  
Floppy disc  $150         $0.50        2.88       $0.17     
QIC          $300         $20          250        $0.08     
Jaz drive    $600         $125         2,000      $0.0625   
9 track      $? (2)       $10          160        $0.06     
CD-R (3)     $100         $12          660        $0.018    
Hard disc    $100         $100  (1)    8,200      $0.01     
DLT (4)      $4,000       $70          30,000     $0.002    
8mm [video]  $2,200       $9           5,100      $0.0018   
4mm [DAT]    $1,800       $7           5,500      $0.0013   

8.2 Utilities.

8.3 Backup Model.

A useful backup model suggested by 3M is the "Grandfather, Father, Son" principle. This scheme uses a total of ten units of backup media (where a unit is sufficient to backup the entire system) to provide up to twelve weeks of coverage.

Label ten sets of media with these labels: Monday, Tuesday, Wednesday, Thursday, Friday 1, Friday 2, Friday 3, Month 1, Month 2, Month 3.

Start the cycle on a Friday. Do a full backup onto the Friday 1 media.

Every Monday through Thursday, use the appropriately labelled media to do an incremental backup.

Each Friday, use the next Friday media set to do another full backup, continuing to use the Monday through Thursday incremental scheme.

Every forth Friday, use one of the monthly media sets (Month 1 through Month 3) to do the full backup.

After four months you start the sequence over again. Write the date used on the media each time, and watch error rates, to ensure you recycle tapes before they become unreadable.Backup Model (Example).

Table 5: Example Backup Schedule 
Monday     Tuesday  Wednesday  Thursday  Friday   
Monday     Tuesday  Wednesday  Thursday  Friday1  
Monday...  ...                           Friday2  
...        ...                           Friday3  

8.4 Copying partitions/portions of file systems.

# dump 0df 100000 - /oldtree | 
(cd /newtree; restore xf -)
Specify a very high density parameter (d 100000) to make dump think it's dumping to a very high-capacity "tape." Otherwise, dump may stop in mid-copy and demand that you mount a new "tape."

# (cd /oldroot; tar cvf - ./dir) |
(cd /newroot; tar xf -)

8.5 Determining a backup strategy

Assumption: The next time you sit down at your system, you find that the hard drive has crashed or a cracker has done an "rm -rf /" while you were gone.

8.6 Example Problems

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