The Design and Implementation of a Log-Structured File System - PowerPoint by OGB7iQ5i

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									                               Embedded System Lab.




The Design and Implementation of
  a Log-Structured File System

             전정호
      dream_back@naver.com



                        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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