Data Triplication:Home and Two Backups S:Site availability e.g,99% F;backup1 L:Link availability e.g,95% 10 User A=SL +(1-SL)SL+(1-SL)2SL S4 Primary site Backup1 Backup2 can be reached can be reached can be reached Primary and 18 Primary site backup1 inaccessible inaccessible Triplicated avail.3SL-3(SL)2-(SL)3 Unavailability 1-3SL -3(SL)2+(SL)3 Fhome F;backup2 =(1-SL)3=0.02% Data unavailability reduced from 5.95%to 0.02% Availability improved from ~94%to 99.98% Part.1.16 Qiang Xu CUHK,Fall 2012
Part.1 .16 Qiang Xu CUHK, Fall 2012 Data Triplication: Home and Two Backups S0 S1 S3 S2 S4 L1 L0 L2 L3 L4 L5 L6 L7 L8 L9 Data unavailability reduced from 5.95% to 0.02% Availability improved from 94% to 99.98% Triplicated avail. = 3SL – 3(SL) 2 – (SL) 3 Unavailability = 1 – 3SL – 3(SL) 2 + (SL) 3 = (1 – SL) 3 = 0.02% S: Site availability e.g., 99% L: Link availability e.g., 95% Fi home Fi backup 2 User Fi backup 1 A = SL + (1 – SL)SL + (1 – SL) 2SL Primary site can be reached Primary site inaccessible Backup 1 can be reached Primary and backup 1 inaccessible Backup 2 can be reached
Data Dispersion:Three of Five Pieces Piece0 A=(SL)4+4(1-SL)(SL)3+6(1-SL)2(SL)2 So 10 Piece4 5 User All 4 pieces Exactly 3 pieces Only 2 pieces can be reached can be reached can be reached Piece 1 S:Site availability e.g,99% L:Link availability e.g,95% 18 Dispersed avail.6(SL)2-8(SL)3 3(SL)4 11 Availability 99.92% S2 Unavailability 1-Availability =0.08% Piece 3 Piece 2 Scheme-> Nonredund. Duplication Triplication Dispersion Unavailability 5.95% 0.35% 0.02% 0.08% Redundancy 0% 100% 200% 67% Part.1.17 Qiang Xu CUHK,Fall 2012
Part.1 .17 Qiang Xu CUHK, Fall 2012 Data Dispersion: Three of Five Pieces S0 S1 S3 S2 S4 L1 L0 L2 L3 L4 L5 L6 L7 L8 L9 Scheme → Nonredund. Duplication Triplication Dispersion Unavailability 5.95% 0.35% 0.02% 0.08% Redundancy 0% 100% 200% 67% Dispersed avail. = 6(SL) 2 – 8(SL) 3 + 3(SL) 4 Availability = 99.92% Unavailability = 1 – Availability = 0.08% S: Site availability e.g., 99% L: Link availability e.g., 95% Piece 3 Piece 2 User Piece 0 A = (SL) 4 + 4(1 – SL)(SL) 3 + 6(1 – SL) 2 (SL) 2 All 4 pieces can be reached Exactly 3 pieces can be reached Only 2 pieces can be reached Piece 1 Piece 4