X-Git-Url: https://git.adam-barratt.org.uk/?p=mirror%2Fdsa-wiki.git;a=blobdiff_plain;f=input%2Fhowto%2Finstall-ganeti.creole;h=d88f02401053b5693d42b1b42419e7210a6bd7d0;hp=2f21981717f82ced1fcd20bd9b559760d4f4bf35;hb=d5c1bab6fdc143193345d7d1d73533ad45e10b1a;hpb=e108c25cba254c48829df890b79a8880fd503304

diff --git a/input/howto/install-ganeti.creole b/input/howto/install-ganeti.creole
index 2f21981..d88f024 100644
--- a/input/howto/install-ganeti.creole
+++ b/input/howto/install-ganeti.creole
@@ -483,6 +483,16 @@ both the network and disk speed allow that.
 }}}
 
 
+=== 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.