Embedded System Lab The Design and Implementation of

Embedded System Lab. The Design and Implementation of a Log-Structured File System Mendel Rosenblum and John K. Ousterhout ACM Transactions on Computer Systems, Vol. 10, Issue 1, pp. 26~52, 1992 정영진 cyj 4369@gmail. com

정 영 진 Embedded System Lab.

Contents l l l Introduction Log-structured file system Simulation Crash recovery Evaluation Conclusion 정 영 진 Embedded System Lab.

Introduction l A gap between processor and HDD http: //blogs. msdn. com/b/e 7/archive/2009/01/25/disk-defragmentation-background-and-engineering-the-windows-7 -improvements. aspx 정 영 진 Embedded System Lab.

Introduction l Internal structure of HDD £ Two components of disk performance l l Transfer bandwidth Access time Chris Ruemmler and John Wilkes. An introduction to disk drive modeling. IEEE Computer, 27(3): 17– 28, March 1994. 정 영 진 Embedded System Lab.

Introduction l Workloads £ Small file l l £ Large file l l £ Limited by the bandwidth of the I/O Limited by memory subsystems LFS l 정 영 진 Office, engineering applications, etc … ‘Metadata’ Focus on the efficiency of small file Embedded System Lab.

Introduction l Problem with existing file systems £ Example of current file system l £ Spread information l £ Cause too many small access Synchronous write l request 정 영 진 Unix FFS File system metadata write request write Embedded System Lab.

Log-structured file system l Fundamental idea £ Asynchronous write request £ write Writing all the changes to disk sequentially l l 정 영 진 Buffer File data, attributes, index blocks, directories, … Single operation Embedded System Lab.

Log-structured file system l LFS(Log-structured file system) £ LFS stores data permanently in the log £ The log contains indexing information £ Large extents of free space available for writing new data l l l 정 영 진 Segment cleaner Cleaning policy Embedded System Lab.

Log-structured file system l LFS layout £ 512 KB ~ 1 MB Segment http: //home. postech. ac. kr/~kypark/study/fs. html 정 영 진 Embedded System Lab.

Log-structured file system l File location and reading £ Basic structure is same with FFS £ Not fixed inode l l £ 정 영 진 inode map Cached in main memory Compact arrangement Embedded System Lab.

Log-structured file system l Segment cleaning £ Delete and update l £ Threading l £ Makes fragmentation Copying l 정 영 진 Fragmentation Large cost Embedded System Lab.

Log-structured file system l Cleaning policy £ 정 영 진 When? £ How many segment? £ Which segment? £ How to group live blocks? not sensitive Embedded System Lab.

Log-structured file system l Which segment? £ £ Write cost, greedy u : Utilization(fraction of live data, 0 ≤ u < 1) Cost is determined by u Trade off l 정 영 진 Performance & Cost per usable data Embedded System Lab.

Simulation l Access pattern £ Uniform l £ 정 영 진 Same request pattern Hot and cold Embedded System Lab.

Simulation l Simulation result 정 영 진 Embedded System Lab.

Simulation l New cleaning policy £ Cost-benefit policy l 정 영 진 Benefit components : free space, space is likely to stay free Embedded System Lab.

Crash recovery l Crash recovery £ Check point l £ Time check, inode map, last segment pointer, etc … Roll forward l l Use segment summary inode is exist / not exist Crash Roll forward Check point region(fixed) 정 영 진 Embedded System Lab.

Evaluation l Micro-benchmarks(Small file) 정 영 진 Embedded System Lab.

Evaluation l Micro-benchmarks(Large file) 정 영 진 Embedded System Lab.

Conclusion l Performance is as good as previous system or much better. l Not only benefit with many small files but also benefit with large files. 정 영 진 Embedded System Lab.

Reference l l Chris Ruemmler and John Wilkes. An introduction to disk drive modeling. IEEE Computer, 27(3): 17– 28, March 1994. http: //blogs. msdn. com/ 정 영 진 Embedded System Lab.

Q&A 정 영 진 Embedded System Lab.