Hi guys, I've been doing the pre-requisite Google research and I haven't reached a conclusion, so thought I'd ask here. I have an experimental pair of identical XenServers setup with DRBD running over a Gigabit cross-over cable. The only difference is that the primary has a SSD and the secondary is a normal spindle drive.
dd tests on the underlying hardware show: * the spindle server is capable of writing at ~70MB/s * the SSD server at ~250MB/s If I put the primary into drbd standalone mode, I also get about ~250MB/s when writing to the DRBD device. When running in primary/secondary mode, however, we only get around the ~65MB/s mark, which makes perfect sense with protocol C. I was expecting that if I switched to protocol A, I would be able to let the SSD drive write at it's full speed (e.g. 250MB/s) only at the price of the secondary potentially falling a little bit behind, however performance is almost exactly the same with protocol A, B, or C at around 60-70MB/s. I then tried combining that with "on-congestion pull-ahead;" to see if that would allow the primary to write at full speed, but still, same result. Is this simply not do-able for some reason to let the primary write at a faster speed than the secondary? Thank you! Andrew
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