“Dr. David Gilbert was unsure whether journalling filesystems
were intended to merely survive the occassional improper shutdown,
or if users should feel comfortable just powering them down as part
of normal operation. Michael Rothwell pointed out that journalling
filesystems only guaranteed the consistency of data that had been
written prior to shutdown, and that any buffers left unflushed at
power-off would be lost, and any applications not properly exited
could also do bad things. “Journaling mostly means not having to
run FSCK,” he said. Daniel Phillips replied to David at greater
length:
Welllllll
…
crashes tend to produce different
effects from sudden power interruptions. In the first case parts of
the system keep running, and bizarre results are possible. An even
bigger difference is the matter of intent. Tux2 is explicitly
designed to legitimize pulling the plug as a valid way of shutting
down.
…
Being able to shut down by hitting the power switch is a
little luxury for which I
’
ve been willing to invest more than a
year of my life to attain. Clueless newbies don
’
t know why it
should be any other way, and it
’
s essential for embedded devices.
…
”
“Alex Belits strongly disagreed that applications should be
considered broken if they mis-handled sudden shutdowns. …
Elsewhere, Stephen C. Tweedie said in response to Daniel’s
statement that the on-disk filesystem image of journalling
filesystems would remain inconsistent until the journal recovery
program had run… Alan Cox replied tersely, “Which means an
ext3 volume cannot be recovered on a hard disk error.” And Stephen
replied:
hard-readonly, then we need to recover in core, and that’s
something which is not yet implemented but is a known todo
item.
Otherwise, it
’
s not worse than an error on ext2: you
don
’
t have a guaranteed safe state to return to so you fall back to
recovering what you can from the journal and then running an e2fsck
pass. e2fsck groks the journal already. And yes, a badly faulty
drive can mess this up, but it can mess it for ext2 just as
badly.
”