[DRBD-user] DRBD or not DRBD ?

Digimer linux at alteeve.com
Tue Apr 26 19:37:36 CEST 2011

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

On 04/26/2011 01:05 PM, Whit Blauvelt wrote:
>> Matching LVs are not the same LVs. The LV with your VM is a single item,
>> and having it treated as such, which you get with clvmd, will ensure
>> that it's not startable on either node at the same time.
> Okay, that could be valuable. Thanks. How does that layer with DRBD? Is
> there a path from a currently-configured and running lvm system to clvmizing
> it? Red Hat's documentation here:

DRBD is just a block device, so far as LVM is concerned. You will need
to set the filter in lvm.conf to only look for drbd devices though,
otherwise it sees the LVM twice (once on the backing device and again on
the DRBD).

I've got the details on how to do this here:


> http://docs.redhat.com/docs/en-US/Red_Hat_Enterprise_Linux/6/html/Logical_Volume_Manager_Administration/LVM_Cluster_Overview.html
> is only a rough sketch at best. For all the effort going into various
> cluster and cloud scenarios, it amazes me how little is getting written up
> well.

Hrm, I'm not sure about migrating an existing LVM, but I do know that
you need to set the locking type to 3 and mark the LVM as clustered.
When creating the VG, this is done with the 'vgcreate -c y' (which is
the default when the clvmd daemon is running). Converting the VG/LVs
though... That will require research.

>> RHCS's rgmanager is much simpler than Pacemaker, and is well tested and
>> already exists. Writing your own scripts is, I'd argue, a fools errand. :)
> Ah, but running rgmanager on Ubuntu would be even more foolish. My
> preference for Ubuntu as host is off topic, but it's a strong one. The
> configuration files alone needed for all the elements of a good Pacemaker
> install might require more lines of code than a custom script for a
> well-defined, limited situation like mine. And the script, I'd understand.
> The configuration file approach gets into trusting voodoo. Not that much of
> sysadmin work doesn't consist in trusting voodoo....

RHCS on .deb distros is probably a non-started. Are you married to
Ubuntu, or would on consider an RPM based install?

As for Pacemaker; My main argument for it is that it is a well tested,
thought out and supported solution. Your custom scripts would only be
known by you, which would be a problem for an IT manager, I should
expect. ;)

>> I must admit, you lost me somewhat in your reference to emailing people. :)
> Any notable systems events around here result in notices, whether through
> Nagios or independently. 


> Best, and thanks again,
> Whit

Best of luck. :)

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