Re: Problems with many DOMUs on a single DOM0.

[Harry Waddell <waddell%caravaninfotech.com@localhost>]

On Mon, 7 Jan 2013 22:50:40 +0100
Johan Ihrén <johani%johani.org@localhost> wrote:

> Hi Harry,
> 
> On Jan 7, 2013, at 22:18 , Harry Waddell wrote:
...
> 
> > I would suggest you look at your open file descriptor limits to at least 
> > rule out the possibility that xenconsoled is running out of file 
> > descriptors for the pty's it's managing.
> 
> Good idea, and Brian Buhrow suggested the same thing.


A quick heads up. As of 6.0.1, this 

http://gnats.netbsd.org/41660

appears to still be broken. If you are changing the openfiles-cur, you'll still 
need to remove the existing login.conf.db before you run cap_mkdb. 

> > I've been using xen for a long time now -- nearly a decade -- and with each 
> > major version, the console support seems to be improving. Once 4.2 hits 
> > pkgsrc and has a chance to gel a bit, you may want to consider upgrading. 
> 
> Yes, I'm considering that. However, I depend heavily on file-backed DOMUs, 
> and until recently there seemed to be problems with that in Xen 4. So "4.2 
> hitting pkgsrc" is exactly what I'm waiting for. 
> 

I vaguely recall some people saying they found issues with using lvm's but they 
work great for me with netbsd 6+ and xen 4.1.3. 

I'd much rather do this:

lvm lvcreate -L 100G -n spiffy-domU-opt vg00 

than this:

dd if=/dev/zero of=/opt/domain_files/spiffy-domU-opt bs=1024k count=102400

* You can easily shrink an lvm, which is great if the domU is using something 
that
can be reduced in size, like ext4 filesystem. 

* lvm's help to keep the domU's in service from getting I/O starved when new 
virtual disks get created in the dom0. 

* I ran some benchmarks, although I didn't collect enough samples to make it 
scientific, 
using bonnie++ -s 8g, and using lvm backed ext4 filesystems were faster for 
everything except rewriting data. Sequential blocks in and out were noticably 
better for the lvm backed case. I'll be happy to share my notes if people are 
interested. 

The only downside I see to using LVMs for domU storage is that I have to 
scratch my head just a bit everytime I try to transfer the data from one xen 
server to another, and occasionally, I'll use the character device [slow] when 
I meant to use the block device instead. Files are certainly easier in this 
regard. 


> BTW, I notice that there's no xentools pkg at all for Xen 4.1.2, although 
> there is a xenkernel-4.1.2 pkg. Hmm?
> 

you may have some issue with a tag or "something" in your pkgsrc, because 
sysutils/xentools41 has been available for a while. 


Harry Waddell