[DRBD-user] Split brain in a dual primary configuration
martin at isg.si
Fri Oct 30 23:52:32 CET 2009
it's actually being done in such a way. Apparently it even has it's own
manual chapter. :-)
And a blog entry:
I guess that's the way to go. :-)
Martin Gombac( wrote:
> mind that i'm no expert and can be completely wrong but..
> LVM works on top of drbd in active/passive mode only.
> For active/active you need CLVM (and all of that RH Cluster Suite S**t)
> It's the same as with filesystems, if you want to have it mounted on
> many locations at the same time, you need locking, so that no two nodes
> write at the same spot/block at the same time. LVM by itself doesn't
> guarantee that.
> But to inform you, you're not only one who tried that setup. :-) I'm
> currently looking for appropriate solution.
> One might be:
> Disk <-> LVM <-> DRBD[X] <-> domU[X].
> Where each DRBD instance is one virtual machine.
> It would work, only if during live virtual machine migration from host A
> to host B, writing on host B starts _after_ all writing on host A ceases.
> Does anyone know if this would work and if XEN can/will write
> concurrently during live migration on both backing devices (DRBD[X])?
> Jean-Francois Chevrette wrote:
>> On 09-10-30 3:07 PM, Gianluca Cecchi wrote:
>>> the message is self explanatory: in drbd.conf you define the policy to
>>> "disconnect" when you get a split brain (sb) deriving from a 2-primary
>>> And so does drbd...
>> But what else would be more appropriate for such a situation? In fact,
>> that's what we want to do, have both nodes to disconnect. We don't
>> want either of them to become secondary.
>> Is it acceptable to have both nodes remain primaries while they are
>> disconnected and expect them to sync to each other properly when they
>> are connected again?
>>> btw: having you dual primary and LVM, are you using also CLVMD?
>>> Otherwise if you do modifications on one VG (such as add an lv) you
>>> don't see them immediately, because you don't have cluster locking...
>> We are not using clvm. When a new VG or LV is created, we see it
>> immediately on the second node. Maybe Citrix XenServer has a mechanism
>> so that LVM is reloaded on both nodes when a new VM is created on the
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