On Saturday 30 December 2017 08:20:45 Theodore Ts'o wrote: > On Sat, Dec 30, 2017 at 01:03:52PM +0100, Pali Rohár wrote: > > > > Hi! Thank you for detailed information. I have just one more question, > > what should filesystem specific fsck do if is started by -a or -p (or > > with -y) during boot and filesystem structures indicates that last time > > it was successfully (clean) unmounted? Should it scan whole disk and > > check all data (files/directories/structures) for consistency? Or should > > trust for "clean" state and stop? And if stop, how to tell that > > filesystem fsck to really scan whole disk? For example scanning 2TB disk > > is really time consuming, specially at boot time. > > What e2fsck (fsck.extN) does is check to see if the file system has > the "errors/corruptions were detected by the kernel" bit set. If so, > it will do a full check. Otherwise, if time-based or mount-based > criteria is enabled, and exceeded, then e2fsck will do a full check. > Otherwise, it will stop. > > The other thing e2fsck for ext4 file systems will do is to replay the > journal. This is useful because fsck will run fsck in parallel, while > mount -a mounts file systems serially. So running the journal in > parallel when you have multiple disk spindles can be a big win. This > may be less of a big deal these days since systemd will run mounts in > parallel. > > As far as time-based or mount-based full checks (see tune2fs for > discussion on this topic), we don't enable this by default any more in > e2fsprogs. That's precisely because doing full check for 10 TB disk > takes and 60TB RAID arrays takes a long time. The idea of doing mount > based checks goes back to the BSD days, because disks and memory are > really crappy, and so checking to find problems before they become > catastrophic data loss events made sense. These days for big disks, > the cost/benefit ratio doesn't work out as well. > > Also, if you have snapshot support in your file system, you can simply > create a snapshot, and run the fsck on the snapshot. An example of > how to do this can be found here: > > https://git.kernel.org/pub/scm/fs/ext2/e2fsprogs.git/tree/contrib/e2croncheck > > Cheers, > > - Ted Ok, thank you for explanation. In case for a new UDF fsck tool it would also make sense then to not do full check at boot time if filesystem is marked as clean. -- Pali Rohár pali.rohar@xxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe util-linux" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
