Re: Status of resizing/growing dm-multipath devices on the fly

[Mike Anderson <andmike@linux.vnet.ibm.com>]

Pasi K?rkk?inen <pasik@iki.fi> wrote:
> On Wed, Aug 06, 2008 at 03:48:12PM +0200, Domenico Viggiani wrote:
> > * Pasi Kärkkäinen wrote:
> > > 
> > > Is it possible to resize (grow) dm-multipath devices on the 
> > > fly nowadays?
> > > 
> > > I googled and found some discussions about the subject, but 
> > > the conclusion seemed to be it's not possible.. that was a 
> > > while ago, so I was wondering if this has been fixed/implemented..
> > > 
> > > Using LVM and adding another new LUN/PV is not an option 
> > > always.. it's a lot easier to manage the whole thing if it's 
> > > possible to resize/grow existing LUNs on the fly.
> > 
> > Nowadays all disk-arrays make online LUN extension a breeze but
> > unfortunately it seems that dm-multipath is still not able to see new size
> > without downtime:
> >  http://www.redhat.com/archives/dm-devel/2007-August/msg00205.html
> > Look also at this recent thread on RHEL5 mailing-list where you can find
> > also a post from a Red Hat representative:
> >  http://www.redhat.com/archives/rhelv5-list/2008-July/msg00267.html
> > 
> > Sure, you can just add a new LUN, pvcreate and vgextend but it is not a
> > viable solution because it causes LUN proliferation.
> > 
> > Sincerely, I'm still subscribed to this mailing-list only to see if someone
> > solve this SHAME!
> > It's a feature that Linux really needs.
> > 
> > Hope someone pick this cry of pain!
> > 
> 
> Thanks for the reply.
> 
> Does someone know what's the actual problem in this? meaning why it hasn't
> been done yet.. 

It has to do with the block layer not using the new size value while there
are openers.

Andrew submitted a patch series (url below) a while ago to try and address
this issue, but I do not know the status. I added Andrew to the cc.

http://thread.gmane.org/gmane.linux.scsi/41623

-andmike
--
Michael Anderson
andmike@linux.vnet.ibm.com