lars.ellenberg at linbit
Jul 11, 2012, 12:24 PM
Post #4 of 4
On Tue, Jul 10, 2012 at 06:59:36PM +0200, Jean-Baptiste wrote:
Re: Switching from internal to external meta-disk
[In reply to]
> Today I was confronted with this problem :
> I've got a 2 nodes cluster. Both of them uses drbd resource to assume
> The main drbd resource store all the data of an Oracle SGBD.
> To solve my problematic (frequently resize resources), I decided to move
> the drbd metadatas from internal to external volume.
> The sub-layer used is LVM.
> Here is how I was do this :
The starting point is missing.
Have the peers been "Connected UpToDate/UpToDate" ?
> 1. Create new logical volume to store meta-datas
> 2. Unmount the resource to migrate
> 3. Dump the meta-datas to plain file
> 4. Shutdown the resource (drbdadm down <RES>)
> 5. Modify the drbd.conf to use meta-disk external
> 6. Restart drbd daemon
uhm. there is no drbd "daemon" ... but anyways...
> 7. Create md for the resource (drbdadm create-md <RES>)
I don't see the step where you restore the previously dumped meta data?
> 8. Startup resource
So in 7. you told DRBD that it was a fresh "just created" instance,
without any valid data.
If by "startup resource" you mean "drbdadm up <resource>" (or adjust),
it will connect to the peer, which *does* have valid meta data,
so immediate full sync is started right here, from the peer
to the node where you did "create-md".
> 9. Doing drbdadm -- --overwrite-data-of-peer primary <RES> (from the
> primary node)
Well, of course you can promote a SyncTarget to Primary,
as it has access to the peers data.
But the "--overwrite-data-of-peer" is actually a "--force",
and only relevant if DRBD otherwise would have refused to promote.
Which in this case, it likely would not have, anyways.
> 10. Let synchronize process ending
Without noticing that it was not the expected direction.
> 11. Done
> At this step everything is fine, my SGBD was restarted without any warning,
> nothing seems to go wrong.
> But ... I was lost 11 days of data in my SGBD.
> I'm disapointed, does anyone have an idea about this ?
> At least to explain this.
: Lars Ellenberg
: LINBIT | Your Way to High Availability
: DRBD/HA support and consulting http://www.linbit.com
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