Plans for BTRFS in Fedora

Matthew Garrett mjg59 at
Wed Feb 23 20:33:14 UTC 2011

On Wed, Feb 23, 2011 at 02:08:08PM -0600, Chris Adams wrote:
> Once upon a time, Matthew Garrett <mjg59 at> said:
> > You can't move PVs.
> What do you think pvmove does?

Move PEs from one PV to another. You can't move a PV.

> > You need a separate /boot.
> That's needed for more than just LVM (and probably won't go away, as it
> is a lot simpler to handle a single method in the installer).

Unless you're booting off iSCSI or really, really love software RAID 
(which btrfs also kindly simplifies), the only reason you need a 
separate /boot is because we're slow at putting updated filesystem 
support in grub because there's no need because we default to a separate 
/boot. There's a certain amount of circularity there.

> > If you use more than one 
> > disk then it adds significant fragility to the boot process.
> How does it do that (any more than any other multi-disk setup)?

My experience with LVM is that any number of error states dump me into 
an awkward recovery scenario. Again it's not an inherent problem with 
the technology, more just that because nobody outside the enterprise 
world really cares about LVM nobody has bothered making it easy for 
non-sysadmins to handle this stuff.

> > It slows 
> > down booting.
> Cite numbers?  It was slower early on, but it goes right by now.  I
> don't doubt it adds some time (of course), but I don't see it being any
> significant amount.

Talk to Lennart about it. It's on the order of two seconds.

> > btrfs does the former without anywhere near as much of 
> > the latter.
> Oh, I don't object to btrfs and having the basic volume management in
> the filesystem layer.  AdvFS on DEC Unix was great in that respect.  I
> object to your painting of LVM aw "awful".

My objections to the technology aren't that strong. My objections to the 
user experience are.

Matthew Garrett | mjg59 at

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