Media Backup Rotation Methods


SRSequential Rotation
MonTueWedThuFri
Tape12341
Example: Four tapes
Backup daily.
When reach tape N start again at tape 1
Takes N tapes
Recovery window: 4 days (based on total number of tapes)
  
FSFather-Son
MonTueWedThuFri
TapeABCDFriday 1
Friday 2
Friday 3
Friday 1
Example: Four daily tapes, three Friday tapes
4 Tapes - M-Th
  • Backup on day
N tapes for Friday
  • Perform sequential rotation on the Friday tapes
Takes 4 +N tapes (depending on how many Friday tapes you want)
Daily tapes see more wear
Recovery window: 3 weeks (based on Firday tapes)
  
GFSGrandFather-Father-Son
4 Tapes - M-Th
  • Backup on day
3 tapes for Friday(1-3)
  • Perform sequential rotation on the Friday tapes
3 tapes for Monthly(1-3)
  • when 3th Friday tape is used use next monthly tape
  • Perform sequential rotation on monthly tapes
Cycle repeats every 4 months
Note: no distinction for longer/shorter months than others
Takes 10 tapes
Daily tapes see most wear
Recovery window: 3 months (based on monthly tapes)
  
GGFSGreatGrandfather-GrandFather-Father-Son
4 tapes - M-Th
  • Backup on day
3 tapes for Friday(1-3)
  • Perform sequential rotation on the Friday tapes
3 tapes for Monthly(1-3)
  • when 3th Friday tape is used use next monthly tape
  • Perform sequential rotation on monthly tapes
3 tapes for Quarterly(1-3) - optional
  • Backup on last Friday of March, June, Sept is Quarter 1,2,3 respectivly
3 tapes for Yearly(1-3)
  • Last Friday tape of the year is the yearly tape
  • Perform sequential rotation on yearly tapes
Cycle repeats every 3 years
Note: no distinction for longer/shorter months than others
Needs 13-16 tapes
Requires the most number of tapes
Daily tapes see excessive wear
Recovery window: 3 Years (based on total number of yearly tapes)
  
IRIncremental-Rotation
MonTueWedThuFri
Week 112345
Week 223456
Week 334567
Week 445678
Week 556789
Week 667891
Week 778912
Tapes are numbered 1-N - example is 9
To extend add more tapes at end
Even usage and wear to all tapes
Take N tapes
Each tape adds another week of backup
Recovery window: 5 weeks (N-4) - (based on number of tapes)
  
TOHTower of Hanoi
A
A
 
A
 
A
 
A
 
A
 
A
 
A
 
A
B 
B
   
B
   
B
   
B
 
C   
C
       
C
   
D       
D
       
Example: Four tapes A-D
Minimum number of tapes (N)
Each extra tape doubles the days covered
Most complex of all backup schemes
'A' tape used 2 X more than 'B' tape etc.
Tapes (A) see extreme wear
Recovery window: 2^N or 8 days (based on number of tapes)

Note: Media can be tapes, CD, DVD, USB Hard Drives, NAS units, USB Thumb drives, etc.

Current revision of this document: Last revised:
http://www.wyld-ink.org/media_rotation.html September 28, 2005