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

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

Goal Study various distributed architectures NFS xFS SAN SSFS Conclusion

Direct Attached Storage Data Storage Unit Data on SCCI/Fibre

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

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

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.

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

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

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

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

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

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

Conclusion Why not get two birds in one shot?