[DRBD-user] DRBD, Xen, HVM and live migration

Bart Coninckx bart.coninckx at telenet.be
Fri Sep 23 23:41:33 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 09/23/11 22:20, Arnold Krille wrote:
> On Friday 23 September 2011 21:37:51 you wrote:
>> On 09/23/11 19:03, Arnold Krille wrote:
>>> On Friday 23 September 2011 18:28:41 Felix Frank wrote:
>>>> On 09/23/2011 06:18 PM, Bart Coninckx wrote:
>>>>> Felix,
>>>>> do you combine your setup with clustering software? Or do you script a
>>>>> live migration? I'm intrigued by how you handle the timing in the
>>>>> latter case.
>>>> ah, I didn't make this really clear.
>>>> I haven't set this up with either live migration capabilities nor
>>>> pacemaker. All I have is a hot standby for manual recovery in case of a
>>>> primary node failure. Sorry.
>>>> I believe that for pacemaker, you would have both your nodes be primary
>>>> at all times (i.e., not use a master-slave set at all).
>>>> Not a thrilling perspective, I guess.
>>> Dual primary isn't really needed (but its very nice to have).
>>> If you use one drbd-resource per vm, you need the dual-primary only
>>> during the migration.
>>> You can also run single-master that is exported via iscsi/aoe and mounted
>>> to all nodes, cluster filesystem on top and you also get an extendible
>>> vm- platform. But then you will have vms writing over network to the
>>> other node through iscsi which is writing back to your node via drbd...
>> That is an interesting idea, though it brakes a bit the high
>> availability mission: if one node goes down, you would need to connect
>> to the same node (local iSCSI session). I'm told this is not good. It
>> would be an ideal situation though, except for the additional network
>> cards (seperation iSCSI and DRBD traffic).
> True, local iscsi is not nice. But you can get around this by booting your
> machines from an gpxe-iso/floppy and tell them the iscsi-device via dhcp.

you mean the virtual machines I suppose.
that's actually not a bad idea. thank you!

> is actually a pretty cool solution, it scales to more then two nodes rather
> easily. And when you decide that a vm needs to many resources, you can always
> adopt the mac-addresses in your dhcp-config and boot that iscsi-image on a real
> machine. The "problem" with this solution is that it has that double-network-
> traffic penalty when a vm runs on the drbd-slave, it will send both read- and
> write-requests across the network two times and you loose the advantage of
> drbds local reading. But when your system get big enough, you will probably
> not run the vm's on the drbd machines to optimize performance...

I suppose this can be partially helped by dedicating network cards for 

> Have a nice weekend,

U2, Arnold,


> Arnold
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