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> Von: sander.grendelman@gmail.com =0A=
> Gesendet: Donnerstag, 9. Januar 2014 10:32=0A=
> An: Markus Stockhausen=0A=
> Cc: users@ovirt.org=0A=
> Betreff: Re: [Users] VirtIO disk latency=0A=
> =0A=
> On Thu, Jan 9, 2014 at 10:16 AM, Markus Stockhausen=0A=
> <stockhausen@collogia.de> wrote:=0A=
> ...=0A=
> > - access NFS inside the hypervisor - 12.000 I/Os per second - or 83us l=
atency=0A=
> > - access DISK inside ESX VM that resides on NFS - 8000 I/Os per second =
- or 125us latency=0A=
> > - access DISK inside OVirt VM that resides on NFS - 2200 I/Os per secon=
d - or 450us latency=0A=
> =0A=
> I can do a bit of testing on local disk and FC (with some extra setup=0A=
> maybe also NFS).=0A=
> What is your exact testing method? ( commands, file sizes, sofware=0A=
> versions, mount options etc.)=0A=
=0A=
Thanks for taking time to help. =0A=
=0A=
I have used several tools to measure latencies but it=0A=
always boils down to the same numbers. The software =0A=
components and their releases should not matter to get =0A=
a first overview. The important thing is to ensure that a =0A=
read request of a test inside the VM is really passing the =0A=
QEMU layer. =0A=
=0A=
The simplest test I can think of (at least in our case) is to=0A=
start a Windows VM and attach a very small NFS disk with=0A=
1GB to it. Start it, install HDTune Trial and run the random =0A=
access test to the small disk. Other ways could be to run =0A=
some kind of direct IO based read test inside the VM.=0A=
=0A=
During each test I can see the packets running between =0A=
the NFS server and the hypervisor so I know that each=0A=
request is not cached inside the VM or QEMU. =0A=
=0A=
After one or two runs the filecache in the RAM of our NFS =0A=
server has all the hot data and latency decreases down to=0A=
the microseconds area. With that we can derive the=0A=
penalty of the virtualization layer.=0A=
=0A=
Whatever I try to optimize I only reach 1/4th of the I/Os=0A=
of ESX for very small packets (512 bytes or 1K). And=0A=
that inside the same (migrated) VM on the same NFS=0A=
topology with the same test programs.=0A=
=0A=
The baseline numbers for the hypervisor are an average of =0A=
running direct io based test tools onto files residing on=0A=
the same NFS.=0A=
=0A=
Markus=0A=
=0A=
P.S. I'm not complaining about that performance. =0A=
Driving an IPoIB environment you get used to waste =0A=
bandwidth and latency. But it is always good to know=0A=
where it comes from.=
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