BTRFS concerns (was: Re: Plan for tomorrow's FESCo meeting (2011-06-01))

[Richard W.M. Jones]

On Thu, Jun 02, 2011 at 12:44:46PM -0500, Chris Adams wrote:
> Once upon a time, Josef Bacik <josef at toxicpanda.com> said:
> > These sort of issues are my priority and I've spent the last 2 months
> > specifically working on the kvm performance differences between ext4
> > and btrfs.  Now we're not on par with ext4 yet, but we aren't 2-3
> > times slower any more, maybe at the most we're 20% slower.  Thanks,
> 
> How does it compare to straight LVM for virtual images?  I create a big
> LV and then only use part of it for the host OS VG; when I create VMs, I
> create a VG for each (or I can snapshot an existing "base" VG).
> 
> It is my understanding that one goal for btrfs is to take LVM out of the
> picture for the common case; i.e. btrfs can do its own logical volume
> management.  If that's the case, there needs to be something comparable
> to the VM-on-VG setup (in terms of ease-of-management and performance).

Maybe I'm not understanding your question correctly, but a filesystem
is more general than LVM.  You can create directories corresponding to
your current VGs and files for your LVs, with the advantage that you
can nest directories which you can't do with LVM VGs.

However the performance issue will be critical -- even 5% slower
really matters for VMs.  But I hope btrfs can close this gap because
the filesystem design is really nice.

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
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