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CS 423: Operating Systems Design
Professor Tianyin Xu
CS 423: Operating Systems Design
MP1/MP2/Midterm Stats
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CS 423 Operating System Design: Log-Structured File Systems - - PowerPoint PPT Presentation
CS 423 Operating System Design: Log-Structured File Systems - - PowerPoint PPT Presentation
CS 423 Operating System Design: Log-Structured File Systems Professor Tianyin Xu CS 423: Operating Systems Design MP1/MP2/Midterm Stats CS 423: Operating Systems Design 2 Recap File Disk block Inode To read/write a file, we
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CS 423: Operating Systems Design
Recap
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■ File ■ Disk block ■ Inode ■ To read/write a file, we have to find the
inode of the file first.
■ Sequential reads/writes are MUCH faster than
random reads/writes
■ Why?
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CS 423: Operating Systems Design 4
Alternate figure, same basic idea
Berkeley FFS / UNIX FS
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CS 423: Operating Systems Design
Computers Circa 1991
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■ Disk bandwidth is improving rapidly ■ Computers have more memory (up to 128 MB) ■ And, alas, disk seek times are … still dog slow! ■ The overhead was becoming larger now (as
the bandwidth is higher..)
■ What can we do to solve the problem? ■ Why not we always do sequential I/O?
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CS 423: Operating Systems Design
Thought Experiments
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CS 423: Operating Systems Design
Let’s do a design
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CS 423: Operating Systems Design
Debates
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CS 423: Operating Systems Design
Flash memory
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■ No need for sequential writes
- just need to find unused blocks
■ Can do 1->0 rewrites
- Maintain a bitmap of used blocks at fixed block
■ Lots of complexity
- Bits wear out, read disruption, etc
- Who should deal with those complexity?
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CS 423: Operating Systems Design
Flash memory
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■ No need for sequential writes
- just need to find unused blocks
■ Can do 1->0 rewrites
- Maintain a bitmap of used blocks at fixed block
■ Lots of complexity
- Bits wear out, read disruption, etc
- Who should deal with those complexity?