1 / 12

AFS/Coda

AFS/Coda. System Overview. Server: VICE -> V ast I ntegrated C omputing E nvironment file system Client: Venus -> VIRTUE: V irtue i s R eached T hrough U nix and E macs. Big Picture. Consistency . Whole-file caching/serving Vice tracks copies of files at clients

fauve
Download Presentation

AFS/Coda

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. AFS/Coda

  2. System Overview • Server: VICE ->Vast Integrated Computing Environment file system Client: Venus -> VIRTUE: Virtue is Reached Through Unix and Emacs

  3. Big Picture

  4. Consistency • Whole-file caching/serving • Vice tracks copies of files at clients • stateful server (danger?) • server-based invalidation on file close/update • “callback” • check every t minutes (“lost”) • Session semantics • ~ UNIX

  5. Sharing Files Why not propagate actual update? User may not care about the file anymore …

  6. Client Caching • The use of local copies when opening a session in Coda.

  7. Session Semantics • When good? • Read-only, large files • When bad? • Access a small amt of a large file, lots of sharing

  8. Coda: Higher Availability • Server Replication • More difficult to get partitioned from all servers • Consistency? • Disconnected Operation • If no available servers, attempt to work off of the local cache • Consistency?

  9. Server Replication • read-one, write-all approach • Each client has a preferred server • Holds all callbacksfor client • Answers all read requests from client • Latest version • sole owner: no callbacks are used • NSFv4 has moved closer to AFS

  10. Cache Coherence • Pessimistic: make sure that conflicts cannot arise. • E.g., one user allowed to access a file at a time • Optimistic: allow unconstrained sharing, and then resolve possible conflicts if they arise • An availability vs. consistency tradeoff?

  11. Pessimistic • Consider a policy when one user acquires a file, and owns it until she releases it • Problems? • No one else can access the file, even to read • What if the owner gets disconnected? • Owner disconnection – use timeout (lease)? • What if no one else is using the file?

  12. Optimistic • Anyone can modify anything • What if client is disconnected? • Higher chance of conflicts occurring • Studies show chance of conflicts is very low

More Related