[DRBD-user] Data Block Changes replication with 5 servers

Adam Goryachev mailinglists at websitemanagers.com.au
Sun Nov 12 23:33:37 CET 2017

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


On 09/11/17 05:01, fernandocmachado at yahoo.com.br wrote:
>
> Hello everyone,
>
> I’m trying to implemente the following scenario:
>
> 4 servers running KVM virtual machines and 1 server as a backup of the 
> 4 servers.
>
> I’m trying to implemente the DRBD to replicate the data block changed 
> from the 4 server to this backup server, but I don’t know how to do 
> that, since all the “Howtos” on the internet applies only for 2 nodes 
> replication.
>
> Could anyone help me on this?
>
Yes.

I could add more, but then it probably wouldn't be helpful. On the other 
hand, you could add more information about your environment and it would 
definitely be helpful.
What version of DRBD are you using?
How many copies of the "data blocks" do you want? If it one copy on one 
of the 4 servers plus one copy on the "backup" server?
What is the storage capacity of the 4 servers and the backup?

OK, I'll add some hints...
If using DRBD 8.4:
For each of the four servers, configure DRBD together with the backup 
server. The backup server will need 4 x storage capacity of the other 
servers, you will end up with 2 copies of all data. Best to use LVM to 
create one LV for each remote server, and then use DRBD to connect these.

If using DRBD9:
Just setup DRBD as normal on all 5 nodes, and then use drbdmanage to 
ensure one copy is on the "backup" node and however many copies you need 
are on the other 4 nodes. Possibly, you want 5 copies of data, so all 
machines have a full copy of all data, but probably 5 copies of data is 
going to cause you a lot of problems.

In either case, keep in mind that the backup server is going to need 
enough ethernet bandwidth as well as disk IOPS to be able to write all 
data changes from all 4 nodes. This could massively reduce your overall 
disk IOPS. You should test carefully prior to deployment.

If you do provide more information, then me or someone else can likely 
provide more detailed/helpful advice.

Regards,
Adam
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