[Linux-cluster] Cluster with shared storage on low budget

Gordan Bobic gordan at bobich.net
Tue Feb 15 09:57:18 UTC 2011

Nikola Savic wrote:
> Digimer wrote:
>> First, it will rejoin the other DRBD members. These members will have a
>> "dirty block" list in memory which will allow them to quickly bring the
>> recovered server back into sync. During this time, you can bring that
>> node online (ie: set it primary and start accessing it via GFS2).
>> However, note that it can not be the sole primary device until it is
>> fully sync'ed.
>   If I understand you well, even before sync is completely done DRBD
> will take care of reading and writing of dirty blocks on problematic
> node that got back online? Let's say that node was down for longer time
> and that synchronization can take few minutes, maybe more. If all
> services start working before sync is complete, it can happen that web
> applications tries to write into or read from dirty block(s). Will DRBD
> take care of that? If not, is there way to suspend startup of services
> (web server and similar) until sync is done?

DRBD and GFS will take care of that for you. DRBD directs reads to nodes 
that are up to date until everything is in sync.

Make sure that in drbd.conf you put in a stonith parameter pointing at 
your fencing agent with suitable parameters, and set the timeout to 
slightly less than what you have it set in cluster.conf. That will 
ensure that you are protected from the race condition where DRBD might 
drop out but the node starts heartbeating between then and when the 
fencing timeout occurs.

Oh, and if you are going to use DRBD there is no reason to use LVM.


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