Christoph Anton Mitterer wrote on 2015/11/24 05:43 +0100:
On Tue, 2015-11-24 at 04:35 +0000, Duncan wrote:
I'm a list regular and btrfs user, not a dev, but all the indications
continue to point to _not_ running it automatically at boot, nobody
even
_suggesting_ otherwise.
Sure, I just asked because maybe that would have just been an
anachronism from the days btrfsck was much more alpha.
The btrfs kernel code itself detects and often
corrects many problems, and btrfs check is simply not recommended for
automatic at-boot scheduling -- if the kernel code can't fix it
without
intervention, then the problem is too serious to be fixed without
intervention by some scheduled btrfs check run, as well.
I once had an issue with a btrfs, where the kernel didn't show anything
but btrfsck did...(not the one Qu's currently looking into).
And I though the same is basically the case for other filesystems like
ext.
In fact, take a look at the shipped fsck.btrfs shell-script, based
upon
the xfs one. As both the code and the comments suggest, it's
specifically designed to simply return success
Sure, but that could have simply been forgotten to update...
Thanks for the update on the status in that matter :)
Cheers,
Chris.
Another point of never running btrfsck at boot time is, it's super
SLOOOOOOOOOOOOOOOOOOOW!
And you should have experienced it during the false alert investigation. :)
It's SLOOOOOOOOOOOOOOOOOOW because it will need to iterate all the
metadata of filesystems to make sure every thing devs can think about is OK.
Unlike traditional filesystem (maybe only ext*), it has some dirty flag
in superblock or things like that to indicate a filesystem needs extra
check, and e2fsck will only do comprehensive check if the filesystem is
dirty.
That's why e2fsck can be run at boot time, as most of time, it just
finds the fs is clean and no extra check.
But btrfs doesn't use the old-fashion method, it uses COW to protect
metadata. So btrfsck is only designed to do comprehensive check and it's
very SLOOOOOOOOOOOOW (not to mention sometimes it's buggy and too
sensitive to give false alert).
Thanks,
Qu
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