[DRBD-user] DRBD inside KVM virtual machine

Andreas Hofmeister andi at collax.com
Fri Oct 21 13:43:40 CEST 2011

Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.

On 21.10.2011 12:00, Nick Morrison wrote:
> Am I mad?  Should it work?
It does. We run DRBD + Pcmk + OCFS2 for testing. I would not use such a 
setup in production though.

>    Will performance suck compared with running DRBD directly on the physical machines?  I understand I will probably have high CPU usage during DRBD syncing, as QEMU's IO (even virtio) will probably load up the CPU, but perhaps this will be minimal,

You will see noticeable higher latencies with both, disk and network. 
"macvtap" may help a bit with the latter, without your network 
throughput would be limited too.

>   or perhaps I can configure QEMU to let the VM guest talk very directly to the physical host's block device..

PCI Passthrough is somewhat problematic. Some 
Chipset/Board/BIOS/Kernel/PCIe-Card/Driver combinations may even work, 
but there is a good chance that you will see sucking performance and/or 
unexplainable crashes. Unless you have a LOT of time to track these 
problems, do not use PCI Passthrugh,


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