I agree with the previous poster's response. Assuming you are using protocol C, DRBD is going to wait for the RAID5 array to report the block has been written to disk on both nodes. Since RAID5 is expensive on write's you add more expense with DRBD waiting for each write to be committed to disk.
In addition I will second the barrier and flush optimizations you can make as per Nils. I saw a significant improvement in performance with my 8.3.11 setup this weekend. sndbuf-size 0; let DRBD auto-tune buffer sizes based on what it sees... rcvbuf-size 0; al-extents 1237; no-disk-barrier; I disabled command DRBD's reliance on command queuing on my SATA drives. Now they "flush". During large write operation tests I saw bursts of 200-500MB write activity on the physical drive every 45-50 secs. I don't use local (physical) raid on my NAS. rate 45M; significantly increases verification performance. Instead of 10 days to verify a large volume it is done in 9 hours. I did the necessary calculations to come up with this number so I know I am safe. -- View this message in context: http://drbd.10923.n7.nabble.com/Low-drbd-performance-50-of-raw-disk-tp17316p17353.html Sent from the DRBD - User mailing list archive at Nabble.com. _______________________________________________ drbd-user mailing list [email protected] http://lists.linbit.com/mailman/listinfo/drbd-user
