On Tue, May 28, 2013 at 10:00 AM, Matt Garman [off-list ref] wrote:

On Mon, May 27, 2013 at 09:02:08PM +0200, Roy Sigurd Karlsbakk wrote:

quoted

Short answer: ZFS will guarantee the data is free of errors, but
MD will give you the flexibility of moving between RAID levels and
adding drives to existing RAIDs. I have been working with ZFS with
some 400TB of storage, and I considered using it for my home
server, but chose MD because of the flexibility in there. ZFS
requires you to plan your setup. It allows you to add VDEVs, but
data isn't balanced over the VDEVs. That will required block
pointer rewrite, something that's been talked about for at least
four years, but yet hasn't surfaced.

In the raid-10 case, does Linux MD automatically "reblance" the
data?  I could be wrong, but my understanding is that it will let
you grow the array, but in the same way that ZFS would (for raid10
anyway): the extra space is there, but not striped across the
original disks.

IIRC, as of March or so of last year (2012), kernels gained the
ability to grow MD RAID10 arrays *provided* they are not using the
"far" offset layout (sadly, my favorite).

--
Jon