Would you tell me what would it happened if the system is running ext2 or ext3 ? Which one is easy to fix excepted restore :)

[C. Linus Hicks]

On Thu, 2004-12-02 at 18:31 -0600, Alex White wrote:
> Ext3 has journaling. What this means for you is that the system journals 
>   disc activity so as if somethin' horrible happens; let's say a power 
> failure in the middle of a disc write or something like that, then the 
> journal will ease recovery. The journal allows the system to replay the 
> last actions taken up to the point of failure and then continue on as if 
>   nothing ever happened. Ext3 is the default for Fedora.

Actually, there's more to it than that. There are three different
journaling modes supported by ext3 as quoted from the Linux source tree
in Documentation/filesystems/ext3.txt and please note the default is
metadata only journaling.

Data Mode
---------
There's 3 different data modes:

* writeback mode
In data=writeback mode, ext3 does not journal data at all.  This mode
provides a similar level of journaling as XFS, JFS, and ReiserFS in its
default mode - metadata journaling.  A crash+recovery can cause
incorrect data to appear in files which were written shortly before the
crash.  This mode will typically provide the best ext3 performance.

* ordered mode
In data=ordered mode, ext3 only officially journals metadata, but it
logically groups metadata and data blocks into a single unit called a
transaction.  When it's time to write the new metadata out to disk, the
associated data blocks are written first.  In general, this mode
perform slightly slower than writeback but significantly faster than
journal mode.

* journal mode
data=journal mode provides full data and metadata journaling.  All new
data is written to the journal first, and then to its final location.
In the event of a crash, the journal can be replayed, bringing both
data and metadata into a consistent state.  This mode is the slowest
except when data needs to be read from and written to disk at the same
time where it outperform all others mode.

-- 
C. Linus Hicks <lhicks at nc.rr.com>