1. Nache: Design and Implementation of a Caching Proxy for NFSv4
Bo Zhao
Computer Science and Engineering
The Pennsylvania State University

2. Motivation & Challenge
Enterprises are moving toward distributed operations
Sharing files across office location in wide area
Sharing data
In a uniform, secure, and consistent manner
Across the global enterprise
Reasonably good performance.

3. Related Work NFS and CIFS - work for a LAN
Low latency and high bandwidth
AFS and DCE/DFS – work for a WAN
Uniting disparate file servers into a single logical file system.
Deployment expense – not widely adopted
GPFS or Lustre - high performance & strong consistency
Expensive or difficult to deploy and administer

4. Cache Consistency NFS – close-to-open consistency
When opening a regular file,
the client validates cached data for that file. The client queries the server to determine if the file has changed. Using this information, the client determines if the data cache for the file should be kept or flushed.
When the file is closed,
the client writes any modified data to the server.
No distributed cache coherency or concurrent write management
AFS – rely on client-side caching for performance
Callback to notify the client of updates
Close – changes become visible at the server

5. New features of NFS v4 - COMPOUND RPC
Many NFS operations in a single RPC call
Lower overall network delay
Example:
RPC in NFS Versions 2 and 3
=> OPEN “home/data”
<= OPEN OK
=> READ at 0 for 32768
<= READ OK (32768 bytes)
=> OPEN “home/data”
READ at 0 for 32768
READ OK (32768 bytes)

6. New features of NFS v4 – Client redirection
Client can be redirected to another server
Build servers in distributed wide Area

7. New features of NFS v4 – OPEN delegations
close-to-open consistency
OPEN delegations
Eliminates: the need for the client to periodically check with the server for cache consistency.
when a file is only being referenced by a single client, responsibility for handling most operations (OPEN & CLOSE) is delegated to the client by the server.

8. Read Delegation OPEN, CLOSE and READ requests Handled locally.
All READs
without sending GETATTRs to check cache validity
All LOCK requests
sent to the server
Callback path is established for recalling a delegation
On a conflicting access to a file such as an OPEN for write, RENAME, and REMOVE.
After a delegation has been recalled
the client falls back to traditional attribute checking before reading cached data.

9. Performance of Read Delegation

10. Write Delegation
All OPEN, READ, WRITE, CLOSE, LOCK, GETATTR, SETATTR requests
Handled locally
On a conflicting OPEN by another client
The server recalls the delegation
Client commits all dirty data and return the delegation.
The conflicting OPEN is delayed until the delegation recall is complete.

11. Performance of Write Delegation

12. Nache vs Redirection In federated system
Data on different geographically distributed physical locations
Two models for data access
Client redirection
Data shipping
Reduce frequent WAN access

13. Nache Architecture
the Nache proxy sits in between a local NFS client and a remote NFS server caching the remote data closer to the client. Nache acts as an NFS server to the local client and as an NFS client to the remote server.

14. Performance of Read and Write Delegations

15. Benefits of Nache

16. Effect of Proxy on response time over a WAN