Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.
"in dual primary mode, only protocol C is allowed. cluster file system deals with cache coherence, DRBD has to deal with storage coherence. you cannot do that asynchronously. to do that in protocol B, the receiving node would need to be able to access data of in-flight requests, which is not implemented." But what if you're not using a filesystem? What if you're just exporting drbd block, active-active devices via say, iscsi or SAS target? Couldn't the initiator just treat them as the same disk, multipathed? In which case if one of your two DRBD nodes goes down, all you care about is that the second node has the writes in memory (because if the second goes down at the same time you're hosed anyway).