On each node, configure lvm to ignore drbd devices and to prefer
{{{/dev/cciss}}} devices names over {{{/dev/block}}} device names
-([[http://code.google.com/p/ganeti/issues/detail?id=93|why?]]):
+([[https://code.google.com/p/ganeti/issues/detail?id=93|why?]]):
{{{
ssed -i \
gnt-cluster command "echo 1 > /sys/bus/pci/devices/0000:0e:00.0/cciss0/rescan"
}}}
+
+=== DRBD optimization ===
+
+The default DRBD parameters are not really optimized, which means very slow (re)syncing. The
+following commands might help to make it faster. Of course the max speed can be increased if
+both the network and disk speed allow that.
+
+{{{
+ gnt-cluster modify -D drbd:net-custom="--max-buffers 36k --sndbuf-size 1024k --rcvbuf-size 2048k"
+ gnt-cluster modify -D drbd:c-min-rate=32768
+ gnt-cluster modify -D drbd:c-max-rate=98304
+ gnt-cluster modify -D drbd:resync-rate=98304
+}}}
+
+
+=== Change the disk cache ===
+
+When using raw volumes or partitions, it is best to avoid the host cache completely to reduce data copies
+and bus traffic. This can be done using:
+
+{{{
+ gnt-cluster modify -H kvm:disk_cache=none
+}}}
+
+
=== Change the CPU type ===
Modern processors come with a wide variety of additional instruction sets (SSE, AES-NI, etc.) which vary from processor to processor, but can greatly improve the performance depending on the workload. Ganeti and QEMU default to a compatible subset of cpu features called qemu64, so that if the host processor is changed, or a live migration is performed, the guest will see its CPUfeatures unchanged. This is great for compatibility but comes at a performance cost.