[DRBD-user] Slow Reads on VM - Xenserver and DRBD

Christian Balzer chibi at gol.com
Tue Jul 24 11:11:48 CEST 2012

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

On Tue, 24 Jul 2012 09:40:17 +0200 Felix Frank wrote:

> On 07/24/2012 06:14 AM, Christian Balzer wrote:
> >> > Can you help me? Windows VMs have shown the same issue. 
> > That clearly looks like some Xen deficiency or configuration issue,
> > can't help you with that, sorry.
> > 
> That reminds me - I've once heard a talk on just why Xen has I/O
> performance issues. It's because of the way syscalls are handled among
> DomU kernel, Dom0 kernel and hypervisor.
Yeah, I've read the same thing and am leaning towards KVM for a fully 
virtualized system, though Vserver and (in the future) LXC work for 90% of
the requirements I have.

> Finally: hdparm? Isn't that limited to the old IDE kernel drivers? Are
> you using those? If so - why?
While I certainly wouldn't recommend hdparm as generic storage
and filesystem performance measuring tool (bonnie++ comes to mind), it does
the "right" thing for read tests, more or less.
# hdparm -t /dev/drbd0

 Timing buffered disk reads: 2114 MB in  3.01 seconds = 702.38 MB/sec
That clocks in about 15% (100MB/s) slower than my bonnie tests, but it's
at least in the same ballpark. So the numbers he's seeing are
unfortunately correct AFAICT.


Christian Balzer        Network/Systems Engineer                
chibi at gol.com   	Global OnLine Japan/Fusion Communications

More information about the drbd-user mailing list