A Cooperative Internet Backup Scheme [1] Leonid Bilevich Advanced Topics in Storage Systems [1]M....
Transcript of A Cooperative Internet Backup Scheme [1] Leonid Bilevich Advanced Topics in Storage Systems [1]M....
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A Cooperative InternetBackup Scheme [1]
Leonid Bilevich
Advanced Topics in Storage Systems
[1] M. Lillibridge, S. Elnikety, A. Birrell, M. Burrows, and M. Isard, A cooperative Internet backup scheme, Proc. USENIX Annual Technical Conference, San Antonio, TX, June 2003.
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Outline
• Problem• Main findings• Technical description of the results• Possible extension• Conclusion
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Problem AddressedNeed: BackupConstraint: Small budget
Solution:Peer-to-peer network
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Main Findings
The suggested system is:– Cheap– Reliable– Secure
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Main Features of the System
• Pros:– Cheapness (the hardware is available)– Diversification (different sites and different operation systems)
• Cons: – Unreliability of one computer– Non-cooperative environment
----------------------------------------------------• Solution:
– Redundancy Reliability– Security mechanisms
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The simplified scheme(cooperation)
• Each computer runs a backup program• Partner computers agree on amount of storage and uptime
Main Steps• Backing up data• Restoring data
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Reed-SolomonErasure-Correcting Codes
Backing up data
Restoring data
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Reliability and OverheadExample• Reliability of computer=• Reliability of the system:
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Security
• Confidentiality• Integrity• Free-rider attacks
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Confidentiality• Encrypt the data before sending
Integrity• Authenticate the partner with secret key• Use a keyed cryptographic hash as checksum
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Free-rider attacksAgreement violations• Problem: Using backup service without contributing backing service• Solution: “challenge” – testing if the data is stored
Exploiting the grace period• Problem: The grace period when the computer can be down is exploited• Solution: Read prohibition (using low-utility blocks)
Bandwidth theft• Problem: Computers are used to broadcast information• Solution: Quota on number of reads and writes per day
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Performance
• The network + remote disk step consumes the largest portion of backup time.
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Cost
• For existing Internet backup system: minimal cost$/GB/month• For the new system: minimal cost US cents/GB/month-------------------------------------------------------------------------------------------------------• Saving: times
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Limitations
• Limited grace period• Restoration is impossible during the grace period• Long restoration time• Vulnerability to catastrophic viruses-------------------------------------------------------------------------• Solution: hybrid system with central server
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Other systems
Old systems• Eternity Service• Archival Intermemory• Free Net• Free Haven
New systems• PAST• OceanStore• Pastiche
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Possible extension
Present work – occasional testing• We merely verify that computers don’t drop data.
Another work – rigorous testing• The disk scrubbing technique [2] verifies the integrity of data.--------------------------------------------------------------------------------------------------------------Combined approach• We can incorporate the opportunistic disk scrubbing into the present work,
verifying the validity of data and improving the reliability of the backup system.
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Conclusion
Cooperative Internet backup system• Cheapness• Reliability• Security• Possible extension
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References• M. Lillibridge, S. Elnikety, A. Birrell, M. Burrows, and M. Isard, A cooperative
Internet backup scheme, Proc. USENIX Annual Technical Conference, San Antonio, TX, June 2003.
• J. S. Plank, A tutorial on Reed-Solomon coding for fault-tolerance in RAID-like systems, Software: Practice and Experience, 27(9):995–1012, Sep. 1997. Correction in: J. S. Plank and Y. Ding, Technical Report UT-CS-03-504, Univ. Tennessee, 2003.
• T. J. E. Schwarz, Q. Xin, E. L. Miller, D. D. E. Long, A. Hospodor, and S. Ng, Disk scrubbing in large archival storage systems, Proc. MASCOTS, Volendam, Netherlands, October 2004.