Re: “bio too big” regression and silent data corruption in 3.0

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On Aug  7, 2011, Alexandre Oliva <oliva@xxxxxxxxxxxxxxxxx> wrote:

> 2. Removing a partition from the filesystem (say, the external disk)
> didn't relocate “single” block groups as such to other disks, as
> expected.

/me reads some code and resets expectations about RAID0 in btrfs ;-)

update_block_group_flags is what does this.  It doesn't care what was
chosen when the filesystem was created, it just forces RAID0 if more
than 1 disk remains:

		/* turn single device chunks into raid0 */
		return stripped | BTRFS_BLOCK_GROUP_RAID0;

Is this really intended?  Given my current understanding that RAID0
doesn't mean striping over all disks, but only over two disks, I guess I
might even be interested in it, but...  I still think the user's choice
should be honored, but I don't see where the choice is stored (if it is
at all).


> I wonder, why can't btrfs mark at least mounted partitions as busy, in
> much the same way that swap, md and various filesystems do, to avoid
> such accidental reuses?

Heh.  And *unmark* them when they're removed, too...  As in, it won't
let me create a new filesystem in a partition that was just removed from
a filesystem, if that was the partition listed in /etc/mtab.

-- 
Alexandre Oliva, freedom fighter    http://FSFLA.org/~lxoliva/
You must be the change you wish to see in the world. -- Gandhi
Be Free! -- http://FSFLA.org/   FSF Latin America board member
Free Software Evangelist      Red Hat Brazil Compiler Engineer
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