What is the key difference between stateful and stateless file services?

A stateful server keeps per-client information (open files, file pointers); a stateless one keeps none

A stateless server keeps a table of open files; a stateful one does not

A stateful server needs longer requests than a stateless one

Both keep state but only stateless saves it on disk

Which statement about crash recovery is correct?

A stateless server recovers by just restarting; a stateful server must rebuild state or clients must re-establish it

A stateful server recovers by just restarting

Both need complex recovery of open-file tables

A stateless server must detect and clean orphaned state of crashed clients

Why must operations in a stateless service be idempotent?

Requests may be retransmitted and repeating them must give the same effect

Because the server must remember each client's file pointer

Because requests are shorter and refer to a session id

Because idempotent operations make locking easy

Which pairing is correct?

Stateless: longer requests carrying file id, offset and count, as in NFS (v2, v3)

Stateless: short requests using a session id, as in AFS

Stateful: long requests carrying file id, offset and count, as in NFS

Stateful: no need to track clients, as in NFS

2076 Asoj

DFS; stateless vs stateful services

Short answer

A distributed file system provides transparent, shared access to files across a network. Stateful servers maintain client session state like open files and file pointers, using short requests but complex crash recovery; stateless servers store no client information, each request carries full context, making recovery simple but requiring idempotent operations.

Define Distributed file system. Point out the differences between stateless and stateful services.

Distributed file system

A distributed file system (DFS) keeps files on one or more servers and gives clients on a network access to them as if they were local, with a common name space, transparency, sharing, security and consistency (for example NFS, AFS).

Stateless versus stateful services

Point	Stateful service	Stateless service
Server memory	Keeps information about each client (open files, file pointers)	Keeps no client information
Request	Short; refers to a session or open file id	Longer; each carries file id, offset, count
Crash recovery	Complex; server must rebuild or clients must re-establish state	Simple; just restart
Client crash	Server must detect and clean orphaned state	No effect
Operations	Need not be idempotent	Must be idempotent (repeatable)
Performance	Fewer disk accesses, read-ahead is easier	More overhead per request
Locking	Easy to support	Needs a separate lock service
Example	AFS (callbacks), RFS	NFS (v2, v3)

✓ Answer checked by Claude Opus 5.5 (high effort)

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