File System Client and Server

Transcription

1 COMP Distributed File Systems With Case Studies: Andrew and Google 1 File System Client and Server Server request (e.g., read) response (e.g., file block) Client 2

2 Factors Encouraging Migration of Data to Shared File Systems Mobility (user & data) Sharing Administration Costs Content Management Security Performance??? Backup 3 Chronology of Early File Systems 4

3 Summary of Sprite Study (1991) 5 Summary of NetApp Study (2008) 6

4 Comparison of Studies Windows Unix Windows 7 File Sizes (by % Files Accessed) NetApp Sprite 8

5 File Sizes (by % Bytes Transferred) NetApp Sprite 9 Run Length (by % Runs) NetApp Sprite 10

6 File Lifetimes (by % Files) NetApp Sprite 2 min 24 hrs 11 Modes of Sharing a Single File Sequential Read Sharing two or more read operations do not overlap in time Sequential Write Sharing two or more operations, at least one of which is a write, do not overlap in time Concurrent Read Sharing two or more read operations overlap in time Concurrent Write Sharing two or more operations, at least one of which is a write, overlap in time 12

7 Strong Semantics for Concurrent Write Sharing Writes from multiple writers are atomic subsequent reader sees entire update from one of the writers, never some partial update or merging of multiple updates Readers always see the atomic result of the most recently completed write operation 13 Statistics of File Sharing (Unix) Source: Kistler and Satyanarayanan, Disconnected Operation in the Coda File System, ACM TOCS, vol. 10, no. 1, Feb

8 Statistics of File Sharing (Windows) Shared files 15 Characterization of File Usage File sizes are strongly skewed most files accessed are small most bytes come from large files Reads are more frequent than writes (5:1 2:1) Most files are accesses sequentially and/or entirely Mutation is frequent many file lifetimes are short file data is often modified over short intervals 16

9 Characterization of File Usage (continued) Sharing modes: file read and written by one user (common) file written by one user, read by many (sometimes) file read and written by multiple users (rare) Working sets exist Characterizations may change with type file vs directory system vs user 17 Key Properties of Distributed File Systems Transparency file naming user/data mobility sharing (consistency) semantics protection Scalability performance (clients:server ratio) small workgroups to global enterprises low administrative overhead Fault-Tolerant 18