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

Lyre 4179e1 at gmail.com
Wed Sep 21 14:46:27 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.

So activity log is used only when two nodes are connected ?

I believe SRL in VVR stores the IO write order, so it may contain
serval writes to a same block.

On Wed, Sep 21, 2011 at 8:35 PM, Felix Frank <ff at mpexnet.de> wrote:
> Hi,
> 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.
> HTH,
> Felix

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