[DRBD-user] Preventing initial full sync on new install

Lars Ellenberg lars.ellenberg at linbit.com
Sat Nov 24 19:31:51 CET 2007

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

On Thu, Nov 22, 2007 at 06:00:32PM +0100, Christophe Boyanique wrote:
> Hello,
> I will have to convert a cluster from external bay sharing to DRBD
> duplication and the main concern of the client is to reduce the outage
> as services are in production.
> The documentation states:
> You choose which node shall become Primary for the first time (the one
> with the good data, if you have some), then you do drbdadm --
> --overwrite-data-of-peer primary all. The result is a full
> synchronization of the underlying devices (we call this the initial full
> sync).
> The device is usable right away, so if you have no file system already,
> you should create one now.
> My question is; will the device be usable right away during the initial
> full sync or will it be blocked ?

as you quoted above, and as Stefan Seifert pointed out,
the device _is_ usable right away.

> If the device is not accessible; what is the purpose of this full sync

what is the purpose of the initial sync of a raid1 device?

> as, anyway, the device will be formated right away after the full sync ?

if you have existing data, you'd not want to format it away.

> Is there a way to avoid this initial full sync or to reduce the duration ?

but you should not.

especially in your case, what I'd do is:
 unplug that external bay from one of the nodes.
 attach some new storage to that node.

 configure drbd with external meta data to use the existing data on the
 node that still sees it, make it primary there, and start your

 then start drbd on the node with the newly attached storage,
 and let it sync up.
 now, understand and configure heartbeat.

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