[DRBD-user] Consistency in protocol A

Andreas Bauer ab at voltage.de
Tue Feb 21 00:31:39 CET 2012

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


Hello again,

On a different topic....

I run DRBD Primary/Secondary with protocol A. Because performance is important, and I do not require the Secondary to be up to date to the millisecond. So if bad stuff happens to the primary node, I can expect the secondary node to be more or less up-to-date, depending on the amount of data that was still sitting in primary node's buffers.

Can I reasonably expect the secondary node to be clean in terms of order of writes, i.e. slighly outdated maybe yes but consistent up to that past moment in time?

Let's further assume I want even more performance and disable disk-barriers and disk-flushes on both nodes, disregarding the clear warning in the documentation, and the primary node crashes. Now I understand that consistency in terms of write order is not guaranteed anymore for data on the primary node. So the data on the primary node can be considered junk after a crash / failure.

But the data on the secondary node should still be fine, slightly outdated maybe, but consistent. So as long as the primary node is fenced and the data there invalidated, life should be good. Correct?

thanks,

Andreas



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