Lecture No.
34
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Log Structured File Systems-Advance Operating System-Lecture Slides, Slides of Advanced Operating Systems
Advance Operating Systems is about internal structure of your computer. It discuss concepts of threading, memory management, security, paging, process scheduling, deadlock, trojan and cache. This lecture is part of lecture series for course. It includes: Log, Structured, File, System, Journaling, Transactions, Updated, Operations, Crash, Recovery, Management
Typology: Slides
2011/2012
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Lecture No.
Log Structured File Systems
- Log structured (or journaling) file systems record each
update to the file system as a transaction.
- All transactions are written to a log. A transaction is
considered committed once it is written to the log.
However, the file system may not yet be updated.
Implementation
Add log area to disk.
Always write changes to log first – called write-ahead logging or journaling. Then write the changes to the file system. All reads go to the file system. Crash recovery – read log and correct any inconsistencies in the file system.
File system Log
Issue - Log management
Observation: Log only needed for crash recovery
Checkpoint operation – make in-memory copy of file system (file cache) consistent with disk.
After a checkpoint, can truncate log and start again.
Most logging file systems only log metadata (file descriptors and directories) and not file data to keep log size down.
Current trend is towards logging FS
Fast recovery: recovery time O(active operations) and not O(disk size) Better performance if changes need to be reliable
If you need to do synchronous writes, sequential
synchronous writes are much faster than non-sequential
ones.
Examples:
Windows NTFS
Veritas on Sun
Many competing logging file system for Linux
Linux Virtual File System
Uniform file system interface to user processes
Represents any conceivable file system’s general
feature and behavior
Assumes files are objects that share basic properties
regardless of the target file system
Primary Objects in VFS
Superblock object Represents a specific mounted file system
Inode object Represents a specific file
Dentry object Represents a specific directory entry
File object Represents an open file associated with a process