On 07/20/2009 05:29 PM, Theodore Tso wrote:
Here's a revised proposal for the KCONFIG text.
Hopefully this is balanced about the two sides of the issue, without
explicitly advocating for one choice versus another.
What do people think?
- Ted
Hi Ted,
I think that this is a huge improvement - thanks!
Ric
P.S. Note that date=writeback does not make the filesystem more
"prone to corruption after crashes".
config EXT3_DEFAULTS_TO_ORDERED
bool "Default to 'data=ordered' in ext3"
depends on EXT3_FS
help
If a filesystem does not explicitly specify a data ordering
mode, and the journal capability allowed it, ext3 used to
historically default to 'data=ordered'.
Data=ordered mode is the mode used by most distributions, but can
introduce latency problems in some workloads, especially if there
is a combination of high bandwidth background writes and foreground
processes calling fsync() and waiting for the result. In worst
case scenarios, the fsync() call can 500ms to multiple seconds
to return.
The problem with using a default of data=writeback, however,
is that is that after a system crash or a power failure,
files that were written right before the system went down
could contain previously written data or other garbage.
With data=ordered mode, any blocks in the file will have
been data written by the application, avoiding a possibility
of a security breach, which is especially problematic on a
multi-user system. Note, however, that data=ordered does
not guarantee that the file will be consistent at an
application level; the application must use fsync() at
appropriate commit points in order to guarantee
application-level consistency.
If you have been historically happy with ext3's performance,
data=ordered mode will be a safe choice and you should
answer "y" here. If you understand the reliability and data
privacy issues of data=writeback and are willing to make
that trade off, answer "n".
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