Preserving data Risks for my data conclusion You will lose/corrupt data o better to be able to know when and what o even better if you can repair 8/43 S.Ponce-CERN
Preserving data 8 / 43 S. Ponce - CERN risks consistency safety c/c Risks for my data - conclusion You will lose/corrupt data ! better to be able to know when and what even better if you can repair
Preserving data risls consistency safety c/c 花5 Data consistency Risks of data loss and corruption ②Data consistency oChecksums ●Block checksums Data safety Conclusion chsum block 9/43 S.Ponce-CERN
Preserving data 9 / 43 S. Ponce - CERN risks consistency safety c/c cksum block Data consistency 1 Risks of data loss and corruption 2 Data consistency Checksums Block checksums 3 Data safety 4 Conclusion
Preserving data Checksum Definition "small-size datum from a block of digital data for the purpose of detecting errors" n blocks W 6 a1 a2 a3 a4 ..ai. an → CS cksum block 10/43 S.Ponce-CERN
Preserving data 10 / 43 S. Ponce - CERN risks consistency safety c/c cksum block Checksum Definition “small-size datum from a block of digital data for the purpose of detecting errors“ a1 a2 a3 a4 ... ai ... an CS n blocks b w
Preserving data Most basic checksum data size Computation a1 a2 a3 a4 ....aj... an n b=8bit w=64bit CS=n Pros and Contra ●easy to compute o detects erasures and additions o does not detect any corruption cksum block 11/43 S.Ponce-CERN
Preserving data 11 / 43 S. Ponce - CERN risks consistency safety c/c cksum block Most basic checksum : data size Computation a1 a2 a3 a4 ... ai ... an n b = 8 bit w = 64 bit CS = n Pros and Contra easy to compute detects erasures and additions does not detect any corruption
Preserving data Basic checksum sum/xor Computation a1 a2 a3 a4 .ai… an ∑a面 b w=b( CS=ai i=1 Pros and Contra ●easy to compute o detects most corruptions o does not detect any inversions/change of order cksum block 12/43 S.Ponce-CERN
Preserving data 12 / 43 S. Ponce - CERN risks consistency safety c/c cksum block Basic checksum : sum/xor Computation a1 a2 a3 a4 ... ai ... an Pai b w = b CS = Xn i=1 ai Pros and Contra easy to compute detects most corruptions does not detect any inversions/change of order