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ext3 - RedHat Whitepaper confusion.



Below are three paragraphs from the RedHat White paper on ext3. 
The first paragraph says data=ordered is the default mode. The last
paragraph says data=journal is the default mode. Which is correct?

The second paragraph starting on the second line says that to journal
metadata but not file data  use data=ordered or data=writeback,
This contradicts the first paragraph that says that data=ordered
journals data. Which is correct? 

All this is very confusing, is it not? Any clarification would be
appreciated.


1.The second mode, data=ordered (the default mode), guarantees that
 the data is consistent with the file system; recently-written files
 will never show up with garbage contents after a crash.

2. ext3 has multiple journaling modes. It can journal all file data and
 metadata (data=journal), or it can journal metadata but not file
 data (data=ordered or data=writeback). When not journaling file
 data, you can choose to write file system data before metadata
 (data=ordered; causes all metadata to point to valid data), or not
 to handle file data specially at all (data=writeback; file system
 will be consistent, but old data may appear in files after an
 unclean system shutdown). This gives the administrator the power to
 make the trade off between speed and file data consistency, and to
 tune speed for specialized usage patterns.

3. Red Hat is continuing to work on several performance enhancements to
ext3, so you can expect several of these cases to improve in the
future. This means that if you choose data=writeback now, you may want
to retest the default data=journal with future releases to see what
changes have been made relative to your workload.
-- 
-------------------------------------------
Aaron Konstam
Computer Science
Trinity University
715 Stadium Dr.
San Antonio, TX 78212-7200

telephone: (210)-999-7484
email:akonstam trinity edu





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