[DRBD-user] General question about DRBD and HA

Pascal BERTON pascal.berton3 at free.fr
Tue Apr 24 13:39:45 CEST 2012

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


Stefan,

If the master fails, then the slave is promoted master and takes the 
service over. At this time, it's the only node alive. When the former 
master returns to life, its data will be outdated compared to the 
current master. When it joins again the cluster, DRBD will detect that 
inconsistency and sync its data (former master datas) against the 
official master one (current master). DRBD embeds a bitmap scheme to 
identify the outdated datas, it knows precisely what is up to date and 
what is not. There are a couple of pages discussing that by the end of 
the DRBD Users Guide.

Best regards,

Pascal.

Le 24/04/2012 08:17, "Stefan Günther" a écrit :
> Hello,
>
> on the DRBD homepage I found the following sentence:
>
> "After an outage of a node DRBD automatically resynchronizes the 
> temporarily unavailable node to the latest version of the data, in the 
> background, without interfering with the service running."
>
> In a HA scenario where the master server has gone down, DRBD takes 
> care of syncing the data from slave to master.
> But how does the HA software know, when syncing has finished, so that 
> the master server can take his role again?
> I know this is not a DRBD question, but I guess that somehow DRBD has 
> to tell the HA software, that everything is okay again. Silly question?
>
> Thanks for any hints/advice,
>
> Stefan
>
>
>
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