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Distributed File Systems
- 1. 03-10-09 Some slides are taken from Professor Grimshaw, Ranveer Chandra, Krasimira Kapitnova, etc
- 63. User process –> open file F The kernel resolves that it’s a Vice file -> passes it to Venus D is in the cache & has callback – > use it without any network communication D is in cache but has no callback – > contact the appropriate server for a new copy; establish callback D is not in cache – > fetch it from the server ; establish callback File F is identified -> create a current cache copy Venus returns to the kernel which opens F and returns its handle to the process
Editor's Notes
- File is a named collection of related information that is recorded on some permanent storage
- Access transparency – Use same mechanism to access file whether it is local or remote, i.e., map remote files into local file system name space
- Harder to mark failure Performance issues – caching etc? Can’t really do
- COTS Legacy apps Does it really matter where it is? One copy versus many copies Etc
- Lampson –hints for push model
- A server exports one or more of its directories to remote clients Clients access exported directories by mounting them The contents are then accessed as if they were local
- Pros: server is stateless, i.e. no state about open files Cons: Locking is difficult, no concurrency control
- No consistency semantics – things marked dirty flushed within 30 seconds Checks non-dirty items every 5 seconds Bad performance with heavy load etc
- User process wants to open a file with a pathname P The kernel resolves that it’s a Vice file & passes it to Venus on that workstation One of the LWP’s uses the cache to examine each directory component D of P… When processing a pathname component, Venus identifies the server to be contacted by examining the volume field of the Fid. Authentication, protection checking, and network failures complicate the matter considerably.