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Ext4 to be standard for Fedora 11, Btrfs also included (heise online)

Ext4 to be standard for Fedora 11, Btrfs also included (heise online)

Posted Jan 25, 2009 23:56 UTC (Sun) by nix (subscriber, #2304)
In reply to: Ext4 to be standard for Fedora 11, Btrfs also included (heise online) by Nelson
Parent article: Ext4 to be standard for Fedora 11, Btrfs also included (heise online)

UNIX doesn't define semantics for what happens when you lose power
mid-write. That means that what a filesystem does when that happens is a
quality-of-implementation issue: but given that power supplies are not
perfectly reliable it's a fairly important one, especially in countries
like the USA with a third-world electricity distribution network (as a UK
resident I'm privileged to have a fairly reliable power supply and the
most badass electrical regulations on earth: it's one of the few things
the UK's done right infrastructure-wise).

However, I'm afraid I consider 'files you were writing right now might be
chewed up' to be a *lot* better than 'files you were writing right now
might be chewed up, oh, and so might anything else on your disk, even if
you haven't touched it for months'.

I too saw this behaviour when I used XFS (years ago now): I've never seen
it using ext2 or ext3, even when I had multiple consecutive power cuts
during a lightning storm, even when I had bad RAM on the machine and was
doing massive cross-filesystem renames. Of course this too is 'anecdotal':
all reports from third parties are necessarily anecdotal. I don't see how
this makes them invalid (if they come from multiple sources).


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Ext4 to be standard for Fedora 11, Btrfs also included (heise online)

Posted Jan 26, 2009 23:44 UTC (Mon) by lmb (subscriber, #39048) [Link]

Unix/POSIX doesn't define what happens to data in when you crash "mid-write", but it has one hell of an opinion on writes that have been committed and where the write()/fsync()/... calls have returned. So the durable state of the data is quite defined, unless the application is too dumb to make proper use of those features. (And, of course, unless the fs bites the dust.)

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