Embedded System Lab. The Design and Implementation of a Log-Structured File System 전정호 firstname.lastname@example.org Embedded System Lab. Motivation Performance gap Disk seek time : 6.5 ms Problems of other file systems Extendded information Cause many small file (inode, data block) Write synchronously Meta data must synchronization 전정호 Embedded System Lab. Log-Structured File System Segment 512KB ~ 1024KB Disk : consists of segments + checkpoint region segment 0 segment 1 … segment n checkpoint region … Segment summary block Contains each block’s identity : <inode number, offset> Used to check validness of each block Modified times for each block 전정호 Embedded System Lab. Log-Structured File System LFS layout http://home.postech.ac.kr/~kypark/study/fs.html 전정호 Embedded System Lab. Log-Structured File System Different Sprite LFS and Unix FFS 전정호 Embedded System Lab. Log-Structure File System Threading and Copying Use both threaded log and copy and compact Segment cleaning policies when? how many segments? Segment selection policy Block redistribution policy 전정호 Embedded System Lab. Log-Structure File System Write cost u : utilization 전정호 Embedded System Lab. Simulation Result Benefit of cleaning the segment 1 : a cost to read segment Disk = fully 4KB-file u : write back the live data 전정호 Embedded System Lab. Crash recovery Check point Roll-forward checkpoints crash roll-forward 전정호 Embedded System Lab. Experimental results New write Overwrite to creating file existing file 전정호 Embedded System Lab. Experimental results Cleanning overhead Collected over a 4-month period About 70% of bandwidth utilized (write cost 1.2~1.6 : bandwidth 63~83%) Segment utilization of /user6 partition Large number of fully utilized and totally empty segments 전정호 Embedded System Lab. Conclusion LFS is not read performance better than FFS Cleaning the overhead for degrading performance FFS implementation costs less than the LFS 전정호 Embedded System Lab. Q&A 전정호 Embedded System Lab.
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