[DRBD-user] When would acitivity log take effect?

Felix Frank ff at mpexnet.de
Wed Sep 21 14:35:25 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.


good question.

On 09/21/2011 12:23 PM, Lyre wrote:
> Hi all:
> DRBD background resync doesn't promise the IO write order, is that right ?
> However, when would actitivy log take effect? In my opinion, it is
> similiar to SRL in VVR. But I'm confused, I'm curious how does it
> work.
> Considering this situtaion:
> Oracle runs on Primary node (node1) , while secondary node (node2) disconnected.
> when I connect the drbd on node2, the background resync begin.  If
> node crashed during background sync, could it be possible to bring the
> oracle up no node2? Or is there a way to keep the secondary
> consistent? SRL in VVR was able the keep the IO write order.

I'm not familiar with that technology, but with DRBD, this cannot work.

The problem isn't with write order alone. If a block is written multiple
times, the data of the earlier writes is lost. DRBD won't keep some sort
of stash and keep several revisions for single blocks (imagine the cost!).

So no - whenever a resync becomes necessary, you are faced with an
inconsistent SyncTarget as long as the sync is not completed.
DRBD won't allow you to access this data, which is the only sane thing
to do, really.


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