Messages in this thread |  | | Date | Wed, 03 Jan 2001 17:27:25 +0100 | From | Daniel Phillips <> | Subject | Re: Journaling: Surviving or allowing unclean shutdown? |
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Rik van Riel wrote: > > On Wed, 3 Jan 2001, Dr. David Gilbert wrote: > > > I got wondering as to whether the various journaling file > > system activities were designed to survive the occasional > > unclean shutdown or were designed to allow the user to just pull > > the plug as a regular means of shutting down. > > 1. a journaling filesystem is designed to be "consistent" > (or rather, easily recoverable) all of the time > 2. there's no difference between the "2 situations" you > describe above
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. Metadata-only journalling filesystems are not designed to be used this way, and even with full-data journalling you should bear in mind that your on-disk filesystem image remains in an invalid state until the journal recovery program has run successfully. You would not want to upgrade your OS with your filesystem in this state, nor would you want to remove a disk drive that didn't have the journal file on it.
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.
I don't doubt that if the 'power switch' method of shutdown becomes popular we will discover some applications that have windows where they can be hurt by sudden shutdown, even will full filesystem data state being preserved. Such applications are arguably broken because they will behave badly in the event of accidental shutdown anyway, and we should fix them. Well-designed applications are explicitly 'serially reuseable', in other words, you can interrupt at any point and start again from the beginning with valid and expected results.
-- Daniel - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org Please read the FAQ at http://www.tux.org/lkml/
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