Wiera: Towards Flexible Multi-Tiered Geo-Distributed Cloud Storage Instances Zhe Zhang

CAP Theorem For distributed system, “P” is an imperative property Tradeoff between “A” and “C”

Cost Model in AWS Cloud providers use cost model to charge customers There exists a tradeoff between cost and speed

Agenda Introduction Dynamic Consistency Dynamic Primary Locations Reducing cost with Multi-tier storage Exploiting Remote Storage Tiers Conclusions

Agenda Introduction Dynamic Consistency Dynamic Primary Locations Reducing cost with Multi-tier storage Exploiting Remote Storage Tiers Conclusions

Wiera Architecture Wiera User Interface: coordination Global Policy Manager: user-defined policies Tiera Server Manager: mange Tiera instances

Agenda Introduction Dynamic Consistency Dynamic Primary Locations Reducing cost with Multi-tier storage Exploiting Remote Storage Tiers Conclusions

Strong Consistency and Weak Availability put a C c User a sends put request

Strong Consistency and Weak Availability lock B b A put a C c User a sends put request Get a global lock

Strong Consistency and Weak Availability lock B b A put a C c User a sends put request Get a global lock Synchronously updating the object in B and C

Strong Consistency and Weak Availability response a C c User a sends put request Get a global lock Synchronously updating the object in B and C Release the lock and response to user

Strong Consistency and Weak Availability get b A get a C get c User a sends put request Get a global lock Synchronously updating the object in B and C Release the lock and response to user Users start reading from all replications

Weak Consistency and Strong Availability put a C c User a sends put request

Weak Consistency and Strong Availability put a response C c User a sends put request User a immediately gets response

Weak Consistency and Strong Availability get b A outdated object get a C get c User a sends put request User a immediately gets response Users start reading the object but b, c get outdated version of the object

Weak Consistency and Strong Availability get update b A get a C get c update User a sends put request User a immediately gets response Users start reading the object but b, c get outdated version of the object Updates eventually propagate to B and C

Weak Consistency and Strong Availability get b A get a C get c User a sends put request User a immediately gets response Users start reading the object but b, c get outdated version of the object Updates eventually propagate to B and C Users read consistent object

Medium Consistency and Availability put a C c User a get response after all servers receive the object

Medium Consistency and Availability get b A get a C get c User a get response after all servers receive the object All get requests are forwarded to A

Wiera Solution A tradeoff between latency and consistency Dynamically switch consistency models MultiPrimaries PrimaryBackup EventualConsistency High Latency Strong Consistency Medium Latency Medium Consistency Low Latency Weak Consistency

Dynamic Consistency Reducing latency once MultiplePrimaries goes beyond threshold Recovering consistency when latency meet the requirement

Agenda Introduction Dynamic Consistency Dynamic Primary Locations Reducing cost with Multi-tier storage Exploiting Remote Storage Tiers Conclusions

Imbalanced Traffic on Primary Locations get get USA Asia Primary forwared get

Imbalanced Traffic on Primary Locations get get USA Asia Primary forwared get

Imbalanced Traffic on Primary Locations get get USA Asia forwared get Primary

Changing Primary Maintain good consistency Reduce latency

Agenda Introduction Dynamic Consistency Dynamic Primary Locations Reducing cost with Multi-tier storage Exploiting Remote Storage Tiers Conclusions

Motivation Data popularity follows Zipfian distribution Only a small portion of data are considered as hot data Cold data are rarely accessed Using different storage media for different popularity Hot data need fast access speed Cold data can tolerate low access speed

Tradeoff between Cost and Latency Expensive but Fast Tier1(EBS with SSD) Tier2(EBS with HHD) Tier3(S3) Tier4(S3-IA) Cheap but Slow

Reducing Cost Using Multi-tier Storage Performance of accessing local tier storage Performance of accessing centralized cold storage

Reducing Cost Using Multi-tier Storage Performance of accessing local tier storage Money Saver! 10TB can save $300 Performance of accessing centralized cold storage

Agenda Introduction Dynamic Consistency Dynamic Primary Locations Reducing cost with Multi-tier storage Exploiting Remote Storage Tiers Conclusions

Test Setup get get Azure AWS Primary Backup forwared get Create an Wiera instance on Azure as PrimaryBackupConsistency

Exploiting Remote Storage Tiers Azure VM Azure Azure Disk AWS VM Amzon Azure Memory Amazon AWS Azure

Conclusions Wiera is a robust geo-distributed cloud storage Wiera dynamically change configurations to meet desired metrics: Latency Consistency Cost Criticism: When exploiting remote storage tiers, the author did not try to create PrimaryBackup instance on AWS

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