1. Policies in Distributed Data Storage
Presented by: Ajay Potnis
Professor: Craig E. Wills
December 2000

2. Acknowledgements Professor Craig E. Wills Uresh Vahalia Xiaoye Jiang
Gary Ma
Jiannan Zheng
Yael Melman
Mrunal Potnis
Aditya Potnis

3. Goal Study various distributed architectures NFS xFS SAN SSFS
Conclusion

4. Direct Attached Storage
Data Storage Unit
Data on SCCI/Fibre

5. Direct Attached Storage
Channel I/O Speed
Can select the desired storage
No sharing
No flexibility

6. NFS
Data Storage Unit
Data and Metadata
Data on SCCI/Fibre
File Server

7. NFS Simple client server semantics using LAN/WAN
Server is the owner of file system
Uses RPC for communication
NFS with Mount protocol makes FS locally available
Support for advisory locking using NLM
Caching in memory/on disk improves performance on clients (stale data)
Data can be shared by multiple clients
Administration is easy due to centralization of data
Server can provide scalability, high availability, online maintenance, etc.

8. xFS Client Client and Manager Forward Request Data Storage Unit Data
Data on SCCI/Fibre
Data
Storage Server

9. xFS Server-less architecture (clients, storage servers and managers)
Distributes cache, storage and metadata management over machines
Uses a stateful protocol
Uses Active Messages instead of RPC for communication
Multiple managers could lead to more network traffic
Flexibility adding many clients, managers and storage servers
Client write data to storage server before giving it to another client to avoid consistency problems in failures
Increased circular dependencies and complexities

10. SAN (switched fabric) File Server Data Storage Unit Switch Data Data
Data on Fibre

11. SAN Connects multiple clients to multiple storage drives
Storage can be configured at will
Needs good management tools and good Sys Admin skills
No seamless sharing of same storage by multiple clients/servers

12. SSFS Client 1 Data on SCCI / Fibre 1.Metadata Request 2. Metadata
Data Storage Unit uses SAN
Data on SCCI / Fibre for NAS
Server
2. Metadata
1.Metadata Request
Data on SCCI / Fibre
Client 2

13. SSFS Client-Server-Storage semantics using NAS and SAN
NAS for sharing, SAN for channel I/O speed
File sharing among heterogeneous clients
Concurrent sharing among NAS and SAN clients
Server is the owner of metadata and storage
RPC communication for metadata exchange over network
Caching in memory improves performance on clients (stale data not possible because of callbacks)
Read/Write throughput increased since data goes at channel speed (can use multiple SCSI/fibre paths to write)
Multiple clients can use the same storage device
Scalability, high availability, transparent to applications
Failure recovery built in the protocol

14. Conclusion
Why not get two birds in one shot?