[DRBD-user] DRBD inside KVM virtual machine

Florian Haas florian at hastexo.com
Fri Oct 21 14:33:11 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 2011-10-21 13:43, Andreas Hofmeister wrote:
> 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,

I've never seen a DRBD box, physical or virtual, being CPU bound while
syncing. If you're verifying or using data-integrity-alg with an
expensive shash algorithm then perhaps, but it's much more likely the
machine would still be I/O bound.

> 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,

SCSI pass-through may be an option (a little-know Qemu/KVM feature).
Unlikely to be much better than virtio, though.

Hope this helps,

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