[DRBD-user] Increase HW Raid 5 capacity & DRBD

Lars Ellenberg lars.ellenberg at linbit.com
Wed Aug 1 22:31:03 CEST 2007


On Wed, Aug 01, 2007 at 06:37:35PM +0200, Forum.Maillist at GMX.Net wrote:
> Hi all,
> 
> I have 2 HW 3ware Escalade 4 channel SATA Raid systems. They have been
> running on DRBD 0.7.14 on SuSE Linux 10.0 for the last 2 years with
> minor ailments.

don't use 0.7.14, there are plenty of known bugs in it,
there have been _ten_ maintenance releases since then on the 0.7 branch.
upgrade. seriously.

> I need to increase the capacity of the raids, limited to
> 4 devices. How does DRBD handle a secondary that is larger than the
> primary?  Does it get reduced to the same capacity as the primary?

yes.

> Is so, can it be increased, and how?

failover, add more space to the other box as well,
drbdadm resize (on both nodes; wait for the resync), 
verify it has agreed on the expected size,
resize file system.

> The idea is to increase the secondary raid size, mirror it with the
> primary, secondary all, stop primary, increase the primary capacity,
> then primary the previous secondary, secondary the previous primary and
> mirror. Then the secondary / primary could be swapped if need be. Will
> this work? 

yes.
should be in the mailing list archives as well.

> BTW, how can I ensure that the data on the new primary is mirrored and
> not the empty new secondary is mirrored as empty new primary?

DRBD in Primary state will refuse to become SyncTarget, it would rather
drop the connection (go StandAlone) to prevent data corruption.

to be very sure, if there is all new disks in the secondary,
you could do
on the new secondary:
 drbdadm down all;
 drbdadm attach all;
 drbdadm invalidate all; 

 you should now see in /proc/drbd
  StandAlone Secondary/Unknown Inconsistent

 now do drbdadm adjust all
 and it will start to do a full sync for all drbds from current Primary
 to this freshly invalidated box.

hth.

-- 
: Lars Ellenberg                            Tel +43-1-8178292-55 :
: LINBIT Information Technologies GmbH      Fax +43-1-8178292-82 :
: Vivenotgasse 48, A-1120 Vienna/Europe    http://www.linbit.com :



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