[DRBD-user] online shrinking errors / Centos5 drbd 8.3.1 from Testing

Lars Ellenberg lars.ellenberg at linbit.com
Fri Jun 5 12:39:43 CEST 2009

Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.

On Fri, Jun 05, 2009 at 11:30:25AM +0200, Rainer Traut wrote:
> Lars Ellenberg schrieb:
> > expected, even though not exactly intuitive.
> > just because you resize (shrink) the storage area of DRBD,
> > it does not re-locate its internal meta data.
> > 
> > internal meta data always lives in the last sectors of the device.
> > so your lvresize truncated the device, and drbd tried to access beyond
> > end of device.
> > IO error.
> > detach.
> > 
> >  :(
> > 
> Ok, but afaik I did what the user guide told me:
> http://www.drbd.org/users-guide/s-resizing.html#s-shrinking-online
> And what should I have done to place the metadata at the right position 
> after the filesystem?

internal meta data does not work well with online shrinking.

it _may_ work (read: I think it should work even though it is ugly)
if you
   online-shrink the file system
   drbdadm suspend-io on a primary
	(so there will be no more need to access the meta data!)
   truncate the storage device,
	(which makes the on-disk meta data as used up to now unavailable)
   drbdadm resize
	(detects the new lower level device size, and should relocate
	the meta data)
   drbdadm resume-io

but, regardless wether you shrink or grow, with internal meta data,
if you crash at the wrong time, you need to recreate the meta data.

: Lars Ellenberg
: LINBIT | Your Way to High Availability
: DRBD/HA support and consulting http://www.linbit.com

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