Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.
Hello, I've been reading about the barriers (no-disk-barrier option) in drbd. I understand that when the primary gets a IO completion notification, it will issue a barrier request (actually start a new epoch) to the secondary. However, if the disk of the primary has a write cache, it will immediately issue an IO completion notification, without actually writing the data to the disk. So what happens is that the secondary will use lots of barriers to guarantee the write order of the primary while in fact the primary itself has no guarantee about the order. My conclusion is in contradiction with what is written in the user guide http://www.drbd.org/users-guide/re-drbdconf.html: "When selecting the method you should not only base your decision on the measurable performance. In case your backing storage device has a volatile write cache (plain disks, RAID of plain disks) you should use one of the first two (i.e. barrier or flush)." Can someone point the fault in my reasoning? thanks nicolae