On Tue, Nov 24, 2015 at 04:26:47PM -0600, Eric Sandeen wrote: > On 11/24/15 2:38 PM, Austin S Hemmelgarn wrote: > > > if the system was > > shut down cleanly, you're fine barring software bugs, but if it > > crashed, you should be running a check on the FS. > > Um, no... > > The *entire point* of having a journaling filesystem is that after a > crash or power loss, a journal replay on next mount will bring the > metadata into a consistent state.
Not an actual argument within the discussion, but an interesting observation on a fine distinction: It's interesting to note that there's a difference here between journalling and CoW filesystems. A journalling FS needs a journal replay to become consistent. A CoW FS is _always_ consistent, by design. Now, btrfs has a log that should be replayed after an unclean shutdown, but that's all about the data that got written within the current transaction that wasn't committed, rather than about FS metadata consistency. This means that a read-only mount of btrfs can _actually_ be read-only, not modifying any of the data on the disk, whereas a read-only mount of a journalling FS _must_ modify the disk data after an unclean shitdown, in order to be useful (because the FS isn't consistent without the journal replay). Hugo. -- Hugo Mills | I'll take your bet, but make it ten thousand francs. hugo@... carfax.org.uk | I'm only a _poor_ corrupt official. http://carfax.org.uk/ | PGP: E2AB1DE4 | Capt. Renaud, Casablanca
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