[DRBD-user] GFS2 freezes

Lars Ellenberg lars.ellenberg at linbit.com
Wed Oct 31 10:43:42 CET 2012

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


On Wed, Oct 31, 2012 at 09:33:02AM +0000, Maurits van de Lande wrote:
> Hello Zohair,
> 
> >So If I don't have real fencing device, I can't get a cluster?
> 
> It depends, I have some clusters without fencing, they are mainly for
> virtualization. The cluster is configured not to relocate the services
> in case of  a failure. I do this manually. (all services are
> redundant) The Virtual Machine configuration files are stored on a
> GFS2 file system. I configured this file system to be always available
> (also when quorum is lost). Because I do all the recovering manually
> this does not matter, also no data is written to the GFS2 file system.
> 
> So, you can have a cluster without fencing if a quorum loss does not
> corrupt your data. You should also set the cluster timeout's in such a
> way that even with a WAN connection the cluster does not loose quorum
> during normal operation. (I have not tried this)
> 
> For SAMBA you might need "clustered SAMBA" http://ctdb.samba.org/samba.html

clustered samba on GFS2 via WAN to remote locations with bandwidth constraints,
not to speak of latency and possible flakyness of the link.

very very VERY BAD idea.

cluster file system accros a WAN: already a bad idea.

cluster file system without fencing is a sure subscription to data loss.

Cluster file systems are very sensitive to latency,
both storage latency and network latency (for the DLM component).
So even if you would manage to get it working,
the performance of it would sucksucksuck big time
(on a WAN with bandwidth and latency constraints ...).

In a word: Don't.

Maybe look again why you think rsync does not work for you,
use csync2, couple it with inotify maybe,
look into lsyncd (which does the inotify part, and can by coupled with
both rsync or csync2 or any other similar tool), ...

> Did you have a look at glusterfs? http://www.gluster.org/ It supports
> synchronization (I do not know if it also works over a WAN connection)
> But it has  nothing to do with drbd. The drbd 8.3 branch is very
> mature I do not know if this is the same for glusterfs.
> 
> Best regards,
> 
> Maurits
> 
> 
> Van: drbd-user-bounces at lists.linbit.com [mailto:drbd-user-bounces at lists.linbit.com] Namens Zohair Raza
> Verzonden: woensdag 31 oktober 2012 9:51
> Aan: Felix Frank
> CC: drbd-user at lists.linbit.com
> Onderwerp: Re: [DRBD-user] GFS2 freezes
> 
> So If I don't have real fencing device, I can't get a cluster?
> 
> My requirement is to synchronized two Samba boxes between remote
> locations, I can't use rsync because of bandwidth consumption and
> system processing each time it will run it will go through each file
> and see if it is synced or not.
> 
> While GFS seemed to be the right option, but as two servers are
> distant from each other I can not have fencing device as it may
> experience power outage or network failures quite often.
> 
> What do you guys suggest in such scenario?
> 
> Regards,
> Zohair Raza
> 
> 
> On Wed, Oct 31, 2012 at 12:30 PM, Felix Frank <ff at mpexnet.de<mailto:ff at mpexnet.de>> wrote:
> On 10/31/2012 12:02 AM, Lars Ellenberg wrote:
> >>> Manual fencing is not in any way supported. You must be able to call
> >>> > > 'fence_node <peer>' and have the remote node reset. If this doesn't
> >>> > > happen, your fencing is not sufficient.
> >> > fence_node <peer> doesn't work for me
> >> >
> >> > fence_node node2 says
> >> >
> >> > fence node2 failed
> > Which is why you need a *real* fencing device
> > for automatic fencing.
> ...which is bound to sound more than a little cryptic to the
> uninitiated, I assume.
> 
> An example for a "classical" fencing method is a power distribution unit
> with network access. The surviving node accesses the PDU and cuts the
> power to its peer.
> This is just one example. Similar results can be achieved using
> IPMI/ILOM technologies etc.
> 
> HTH,
> Felix
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-- 
: Lars Ellenberg
: LINBIT | Your Way to High Availability
: DRBD/HA support and consulting http://www.linbit.com

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