"Journaling file systems are safer than traditional file
systems because they keep track of changes applied to the disks'
content on a separate log file. They either commit a change or roll
back in a transactional manner, much like an RDBMS...."
"Imagine now that you are updating a directory entry. You've
just modified 23 file entries in the fifth block of some giant
directory entry. Just as the disk is in the middle of writing this
block there is a power-outage; the block is now incomplete, and
"During reboot, Linux (like all Unix machines) runs a program
called "fsck" (file system check) that steps through the entry file
system validating all entries and making sure that blocks are
allocated and referenced correctly. It will find this corrupted
directory entry and attempt to repair it. There is no certainty
that fsck will actually manage to repair the damage. Quite often,
actually, it does not. Sometimes, in a situation as described
above, all the directory entries can be lost."
"For large file systems, fsck can take a very long time. On a
machine with many gigabytes of files, fsck can run for up to 10 or
more hours. During this time, the system is obviously un-usable and
this represents for some shops an unacceptable amount of downtime.
This is where journaling file systems help."
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