Running XENU on vnodes.

Hi.

I created and partitioned a vnode device and installed
NetBSD to it.
It runs as a XENU host:
disk = [ 'file:/vserv/netbsd/nbsd1,xbd0a,w' ]
My question is how (if) running of XEN in a vnode device
affects
system's speed. I'd like to use such setups in production
enviroment
running mail server and sql server on XENU hosts inside vnd
devices.
Would there be any particual perfomance loss if I chose to
run my XEN
'guests' on vnd devices instead of a separate HD
partition?

Cheers,
Marcin.
 

I've measured (very roughly) on a modern recent P4
 
70 MB/s dd from raw disk
59 MB/s dd from 4 GB file in filesystem on disk
57 MB/s dd from 'raw disk' in domU

So in my case it was slower, but not a big deal.
-- 
        Greg Troxel <gdtir.bbn.com>

On Fri, 28 Apr 2006, Greg Troxel wrote:
> I've measured (very roughly) on a modern recent P4
>
> 70 MB/s dd from raw disk
> 59 MB/s dd from 4 GB file in filesystem on disk
> 57 MB/s dd from 'raw disk' in domU
>
> So in my case it was slower, but not a big deal.

What filesystem was the image in the 2nd and 3rd case on?
Do you happen to have numbers for ffs, ffsv2, lfs, fat?
Would be interesting...


  - Hubert

I am rerunning numbers for dom0/domU on vnodes to be a bit
clearer.

The system is a 3400 Mhz P4, Intel 915 chipset motherboard
with 4 GB
DDR2 RAM.
There are 2 SATA drives:
wd0: drive supports 16-sector PIO transfers, LBA48
addressing
wd0: 372 GB, 775221 cyl, 16 head, 63 sec, 512 bytes/sect x
781422768 sectors
wd0: 32-bit data port
wd0: drive supports PIO mode 4, DMA mode 2, Ultra-DMA mode 6
(Ultra/133)
wd0(piixide1:0:0): using PIO mode 4, Ultra-DMA mode 6
(Ultra/133) (using DMA)

The dom0s filesystems are all in RAID-1 using raidframe, and
ffs.
I might have made the large filesystem ffsv2, but I don't
remember.

dom0 is pretty recent NetBSD current.
The domU I use for this example has the same NetBSD current
code.

All times are from dd if=foo of=/dev/null bs=256k, waiting
at least 10-20s

dom0:
rwd0d		70 MB/s
rraid0d		66 MB/s
/n0/xen/foo-wd0 53 MB/s (for the first 10s or so)
		47 MB/s (over a longer time)

domU:
/dev/xbd0d	52 MB/s
                50.5 MB/s (85s for entire 4GB disk)


While it would be nice to have 70 MB/s in domU, I don't
view the
current situation as a huge problem - my domU is as fast as
many of my
older comptuers.  I have a dom0 with several domUs now, and
heading
for 6-8.  The ability to change virtual disk sizes via files
rather
than raw partitions (not to mention running out of 16 bsd
partitions)
seems worth the slowdown.

It does seem that the Xen disk overhead is very low.

-- 
        Greg Troxel <gdtir.bbn.com>

On Fri, 28 Apr 2006 11:28:01 -0400
Greg Troxel <gdtir.bbn.com> wrote:

> I've measured (very roughly) on a modern recent P4
>  
> 70 MB/s dd from raw disk
> 59 MB/s dd from 4 GB file in filesystem on disk
> 57 MB/s dd from 'raw disk' in domU
> 
> So in my case it was slower, but not a big deal.

What other, more precise way can be used to meassure drives
performance ?
I am thinking of simulating a typical web/mysql/email
system's read/write operations.
Running dd gives you an idea of performance when creating
one single file
but this is not really what happens on hosting enviroment.
Would writing of a script that runs in a timed loop with
multiple dd operations on small files
give a more accurate picture of how the performance gets
affected? 

Cheers and thanks
Marcin.

On Fri, 28 Apr 2006, Greg Troxel wrote:
> The dom0s filesystems are all in RAID-1 using
raidframe, and ffs.
> I might have made the large filesystem ffsv2, but I
don't remember.

Can you see how lfs and fat perform, in comparison for ffs?


  - Hubert

  Can you see how lfs and fat perform, in comparison for
ffs?

I could, but I don't have spare time and this is a
production server.

I have no idea why would anyone want to use FAT.

LFS is interesting, but I'd expect the large file to get
fragmented as
the domU does block IO.  And I don't have a warm fuzzy that
it's
completely stable and reliable, which is more important than
speed.

-- 
        Greg Troxel <gdtir.bbn.com>

On Fri, 28 Apr 2006, Greg Troxel wrote:
> I have no idea why would anyone want to use FAT.
>
> LFS is interesting, but I'd expect the large file to
get fragmented as
> the domU does block IO.  And I don't have a warm fuzzy
that it's
> completely stable and reliable, which is more important
than speed.

I'd actually want to see if FAT's any better when it comes
to 
fragmentation, given that you just create image files once
(ideally), and 
then just rewrite the blocks.


  - Hubert