Xen users - Feb 2008 - Physical disks + Software Raid + lvm in domU

Hi,
I''m trying to setup my box as described below:

- The Dom0 exports two disks as physical devices to the DomU
- DomU use the two devices to assemble a software raid device (/dev/md0)
- On the /dev/md0  I create a lvm volume group and lvm volumes on it.

Everything seems to work fine if the lvm volumes on the DomU are lightly 
used. Under heavy load the DomU freeze up immediately.
The i/o tests are performed with bonnie++

This is the DomU configuration file:

#  -*- mode: python; -*-
kernel   = "/boot/vmlinuz-2.6.18-6-xen-amd64"
ramdisk  = "/boot/initrd.img-2.6.18-6-xen-amd64"
memory   = 256
name     = "apollo"
vif      = [''bridge=xenbr0'']
disk     = 
[''file:/datadisk/vmimages/apollo.img,hda1,w'',''file:/datadisk/vmimages/swap.img,hda2,w'',''phy:/dev/disk/by-id/scsi-SATA_WDC_WD5000AAKS-_WD-WCAS82710754,xvda,w'',''phy:/dev/disk/by-id/scsi-SATA_WDC_WD5000AAKS-_WD-WCAS82710669,xvdb,w'']
ip       = "192.168.0.230"
netmask  = "255.255.255.0"
gateway  = "192.168.0.254"
hostname = "apollo"
root     = "/dev/hda1"
extra    = "4"

Is someone experiencing similar problems?

Regards,

Francesco

 



 


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2008/2/27, Francesco Polzella
<f.polzella@datre.it>:
> Hi,
Hi,
>  I''m trying to setup my box as described below:
>
>  - The Dom0 exports two disks as physical devices to the DomU
>  - DomU use the two devices to assemble a software raid device (/dev/md0)
>  - On the /dev/md0  I create a lvm volume group and lvm volumes on it.
I have the same setup. Which distro do you use?
>  Everything seems to work fine if the lvm volumes on the DomU are lightly
>  used. Under heavy load the DomU freeze up immediately.
>  The i/o tests are performed with bonnie++
Can you post the exact command that you run to perform test with bonnie++?
I''m trying bonnie with this command:

#bonnie -html -m vpstest -s 1000 > vpstest-bonnie.html

in HVM environment with gentoo selinux installed and all seem to works fine.
(I have 3 vps running - 2 linux and 1 windows).

When it finishes I will try with bonnie++ and then I will post the result.

Regards

-- 
Alessandro R.

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Hi,
thanks for your reply,
> I have the same setup. Which distro do you use?
Currently I''m using the following hw/sw configuration (Dom0 and DomU):
	- debian etch 
	- Hypervisor 3.0.3 
	- Kernel 2.6.18-6
	- The VM are paravirtualized (not HVM) due to hardware limitations :(
> Can you post the exact command that you run to perform test with bonnie++?
This is the command I use: 
	bonnie++ -d /testdir -u 0:0 

the first test end with success (writing and reading with putc/getc), the second
one freeze the DomU.


Ciao



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2008/2/29, Francesco Polzella
<f.polzella@datre.it>:
> Hi,
>  thanks for your reply,
:)
> Currently I''m using the following hw/sw configuration (Dom0 and
DomU):
>         - debian etch
>         - Hypervisor 3.0.3
>         - Kernel 2.6.18-6
>         - The VM are paravirtualized (not HVM) due to hardware limitations
:(
My configuration is:

gentoo amd64-2007.0
Xen 3.1
kernel 2.6.20-xen-r6
VM PV and HVM
> This is the command I use:
>         bonnie++ -d /testdir -u 0:0
>
>  the first test end with success (writing and reading with putc/getc), the
second one freeze the DomU.
The test on the vm finishes with success but all other vm crash o_O
Under I/O high workload seem that xen have some problem... Any ideas?

I have had same issue when I was untarring portage-tree on new
installation of gentoo (HVM).
Could this problem be related to LVM mapper or RAID software?


-- 
Alessandro R.

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Alessandro R. wrote:
> 2008/2/27, Francesco Polzella <f.polzella@datre.it>:
>   
>> Hi,
>>     
>
> Hi,
>
>   
>>  I''m trying to setup my box as described below:
>>
>>  - The Dom0 exports two disks as physical devices to the DomU
>>  - DomU use the two devices to assemble a software raid device
(/dev/md0)
>>  - On the /dev/md0  I create a lvm volume group and lvm volumes on it.
>>     
>
> I have the same setup. Which distro do you use?
>
>   
>>  Everything seems to work fine if the lvm volumes on the DomU are
lightly
>>  used. Under heavy load the DomU freeze up immediately.
>>  The i/o tests are performed with bonnie++
>>     
>
> Can you post the exact command that you run to perform test with bonnie++?
> I''m trying bonnie with this command:
>
> #bonnie -html -m vpstest -s 1000 > vpstest-bonnie.html
>
> in HVM environment with gentoo selinux installed and all seem to works
fine.
> (I have 3 vps running - 2 linux and 1 windows).
>
> When it finishes I will try with bonnie++ and then I will post the result.
>
> Regards
>   
OK. There is just no reason to do RAID in a Xen virtualized environment 
unless you''re testing out a driver. Let the Dom0 do all that work, 
because it''s already managing the disk IO anyway. LVM to merge together
different partitions or disks, and exporting an LVM partition for the 
DomU should and does work just fine.


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2008/3/1, Nico Kadel-Garcia <nkadel@gmail.com>:
> OK. There is just no reason to do RAID in a Xen virtualized environment
>  unless you''re testing out a driver. Let the Dom0 do all that
work,
>  because it''s already managing the disk IO anyway. LVM to merge
together
>  different partitions or disks, and exporting an LVM partition for the
>  DomU should and does work just fine.
If you don''t use RAID 1 on your disk how will you protect  your data
against disk failure?

-- 
Alessandro R.

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Alessandro R. wrote:
> 2008/3/1, Nico Kadel-Garcia <nkadel@gmail.com>:
> 
>> OK. There is just no reason to do RAID in a Xen virtualized environment
>>  unless you''re testing out a driver. Let the Dom0 do all that
work,
>>  because it''s already managing the disk IO anyway. LVM to
merge together
>>  different partitions or disks, and exporting an LVM partition for the
>>  DomU should and does work just fine.
> 
> If you don''t use RAID 1 on your disk how will you protect  your
data
> against disk failure?
The somewhat obscured point of the message was: Don''t do RAID in domU.
Do it in
dom0 instead.

BR
/Martin Leben


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2008/3/1, Martin Leben <ml060223@leben.nu>:
> Alessandro R. wrote:
>  > 2008/3/1, Nico Kadel-Garcia <nkadel@gmail.com>:
>  >
>  >> OK. There is just no reason to do RAID in a Xen virtualized
environment
>  >>  unless you''re testing out a driver. Let the Dom0 do all
that work,
>  >>  because it''s already managing the disk IO anyway. LVM
to merge together
>  >>  different partitions or disks, and exporting an LVM partition
for the
>  >>  DomU should and does work just fine.
>  >
>  > If you don''t use RAID 1 on your disk how will you protect 
your data
>  > against disk failure?
>
>
> The somewhat obscured point of the message was: Don''t do RAID in
domU. Do it in
>  dom0 instead.
I have nerver used RAID conf  in  dumU, but I have experienced the
domU crash under heavy I/O workload.




-- 
Alessandro R.

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Nico Kadel-Garcia wrote:
> OK. There is just no reason to do RAID in a Xen virtualized 
> environment unless you''re testing out a driver. Let the Dom0 do
all
> that work, because it''s already managing the disk IO anyway. LVM
to
> merge together different partitions or disks, and exporting an LVM 
> partition for the DomU should and does work just fine.
>
You are right,
I agree that the chosen setup is uncommon and maybe isn''t the right way
to do things on xen. The choice was done because of the use of openfiler
as PV guest. Openfiler let''s you manage physical disks with sw raid and
lvm, but expects to have physical disks to start from. One solution, as 
you propose, is to export an LVM volume to the DomU, but openfiler 
webmin will then force the user to create another Volume Group ( and 
volumes ) into the exported volume.
Doing sw raid and LVM in the openfiler DomU was an attractive solution 
to reach these objectives:
	- easy to recover disks (can be mounted easily since they are simple sw 
raid members with LVM on top)
	- Use of unmodified openfiler webmin

I am aware that in such case the disk performance may drop, but it 
should  work!

Best Regards

Francesco




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