[DRBD-user] Install DRBD on a running system to replicate it

valbzh valferon at gmail.com
Thu Aug 11 11:29:02 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.

Daniel Meszaros wrote:
> Am 10.08.2011 22:10, schrieb valbzh:
>> Hello,
>> I would like to know first if it is possible to install DRBD on a running
>> system (NFS server in my case) in order to link it to an other empty
>> server
>> and sync them.
>> I don't want (can't) shutdown this server and I need to migrate it to a
>> replicated solution without turning it off.
>> Thanks. Val
> Hmm, IMHO the necessary steps would be:
> 1. Find an almost identical machine (hardware).
> 2. Install the system and DRBD onto the new machine. Single primary.
> 3. Set up the DRBD device, create FS and mount it.
> 4. Rsync the data from the old machine to the DRBD device of the new 
> machine and verify if data was synced without errors.
> 5. Set up and start NFS on the DRBD device of the new machine and pass 
> the NFS server function to it. Disable the NFS export on the old one.
> 6. Set up DRBD on the old machine. Secondary.
> 7. Sync both DRBD nodes.
> No need to delete the old NFS export's data unless you don't need the 
> disk space. You can still delete it when you are 100% sure that the new 
> setup works fine.
> If both machines shall be able mounting the DRBD devices you need to use 
> a dual-primary-capable FS like GFS2. Both machines would export the same 
> data - probably nice for failover things. Otherwise you can still have 
> the secondary machine switch to primary mode, mount the DRBD device and 
> start NFS in a failover situation (i.e. the former primary drops the 
> connection).
> I myself am just setting up a dual-primary KVM solution here.
> CU,
> Mészi.
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The problem I have using Rsync is that it will take too much time to sync
the entire NAS and to do it, it is necessary (for consitent data) to have
the exports disabled.

This server exports virtual disks for few kvm machines so I would prefer to
reduce the downtime. 

I'm not interested in dual Primary for now because it seems that clustered
filesystems slow down performances, so I will keep it simple for now,
Primary/Secondary with hearbeat, nfs and a virtual IP to handle the

If I migrate my KVM's to a local storage solution first, I will probably
prefer your rsync solution.

Thank you !

Valentin Feron 
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