Xen users - Mar 2007 - DomU Disk-Intense Operations kill Xen-Server?

Hi!

I am sorry to bother you once again, but I wonder how I can get around the
Xen-Crash I can reproduce when combining two xen systems using a drbd
device... as soon as the raid is working (means we have an high latency
network), the DomU starves (and takes Dom0 with it) instantly (e.g. dd
if=/dev/zero of=/file-in-domU-fs.img

I am not SURE if its a Xen-only problem, however, I''ve never seen that
behaviour before.
I am running Xen 3.0.4-1 in 32-Bit Mode atm and messed around with quite
every setting drbd has to offer.
The funny thing is that I can see (xm top) the peak of the cpu load the
domain creates, but then it just dies.
Is there a way around the CPU-Peak? How to enable synchronous writing? (if
possible)
Is there another fix or Filesystem that does handle these sorts of
networks with more ease? Is this (maybe) a xen problem that could be
addressed in another way?

Weird thing is: that only happens when running the "dd" command inside
a
domU - it doesn''t do ANY harm when invoked directly at dom0''s
drbd
device''s filesystem

So I am sorry to bother you again, but help is highly appreciated :)

Thanks in Advance!

Regards, Bigfoot29

_______________________________________________
Xen-users mailing list
Xen-users@lists.xensource.com
http://lists.xensource.com/xen-users

Just a few additions...

setting the filesystems (mount) to sychronuous mode doesn''t help very
much. It helps for quite small write commands (such as dd without bs
addition) where a A64 4600+ raises to 70%CPU load in Dom0 until it falls
down to 20% when whatever-cache-is-missing is written to disk. When using
the "bs" part in "dd" (eg. bs=128k) you see "xm
top" raise Dom0-CPU to 30%
when you are lucky and then the system freezes.
Seems like "something" has trouble _writing_ _big chunks_ of data _at
once_.
When copying big files, everything is fine. Seems like read/write
operations do not harm - but pure massive write seems to kill
"something"
- my bad that I can''t figure out what gets broken...

This isn''t supposed to be a drbd-Problem itself because it DOES work
when
doing a dd in Dom0 into the same mount; but the problem does also not
occur when using NO drbd - maybe Xen DomUs do have problems with quite
slow (10MB/sec) disks?

I am somewhat helpless... :(

Regards, Bigfoot29

> Hi!
>
> I am sorry to bother you once again, but I wonder how I can get around the
> Xen-Crash I can reproduce when combining two xen systems using a drbd
> device... as soon as the raid is working (means we have an high latency
> network), the DomU starves (and takes Dom0 with it) instantly (e.g. dd
> if=/dev/zero of=/file-in-domU-fs.img
>
> I am not SURE if its a Xen-only problem, however, I''ve never seen
that
> behaviour before.
> I am running Xen 3.0.4-1 in 32-Bit Mode atm and messed around with quite
> every setting drbd has to offer.
> The funny thing is that I can see (xm top) the peak of the cpu load the
> domain creates, but then it just dies.
> Is there a way around the CPU-Peak? How to enable synchronous writing? (if
> possible)
> Is there another fix or Filesystem that does handle these sorts of
> networks with more ease? Is this (maybe) a xen problem that could be
> addressed in another way?
>
> Weird thing is: that only happens when running the "dd" command
inside a
> domU - it doesn''t do ANY harm when invoked directly at
dom0''s drbd
> device''s filesystem
>
> So I am sorry to bother you again, but help is highly appreciated :)
>
> Thanks in Advance!
>
> Regards, Bigfoot29
>
>
>
> ------------------------------
>
> Message: 7
> Date: Tue, 20 Mar 2007 09:43:43 +0530
> From: "Ashit Kumar" <Ashit_Kumar@symantec.com>
> Subject: RE: [Xen-users] How can I create another privileged domian?
> To: "Prabhakar Chaganti" <pchaganti@gmail.com>
> Cc: xen-users@lists.xensource.com
> Message-ID:
> 
<BA9C9E8D6DE58F43B85F33C5FC1E1F260165A925@PUNAXCHEMBPIN01.enterprise.veritas.com>
>
> Content-Type: text/plain; charset="us-ascii"
>
> yes..There will be two privileged users Dom0 and Domx running...
> Thanks and regards
> Ashit
>
> ________________________________
>
> From: Prabhakar Chaganti [mailto:pchaganti@gmail.com]
> Sent: Monday, March 19, 2007 10:03 PM
> To: Ashit Kumar
> Cc: xen-users@lists.xensource.com
> Subject: Re: [Xen-users] How can I create another privileged domian?
>
>
> So will there be two privileged domains (dom0 and domx) running at the
> same time?
>
>
>
> On 3/19/07, Ashit Kumar < Ashit_Kumar@symantec.com
> <mailto:Ashit_Kumar@symantec.com> > wrote:
>
> 	Hi,
> 	We know that Domain0 is the privileged domain.Now as per the Xen
> architecture we can make another DomainX (X>0) to be a privileged
> domain.
>
> 	Now here are a few Questions:
> 	A) How can I make another Domain (apart from Domain0) as a
> privileged host?
> 	B) As per the architecture this new privileged domain can manage
> other Domains.So Can it directly manage the drivers and can the DomainX
> view the drivers of this newly created privileged domain?
>
> 	C) Volume Groups(VG) can be created over the raw storage devices
> on Domain0 and the other VM can access them through this Volume Group.Is
> the same thing happens in the case of this newly created privileged
> Domain too?
>
> 	Thanks and regards
> 	Ashit
>
>
> 	_______________________________________________
> 	Xen-users mailing list
> 	Xen-users@lists.xensource.com
> 	http://lists.xensource.com/xen-users
>
>
>
> -------------- next part --------------
> An HTML attachment was scrubbed...
> URL:
>
http://lists.xensource.com/archives/html/xen-users/attachments/20070320/2b217199/attachment.html
>
> ------------------------------
>
> _______________________________________________
> Xen-users mailing list
> Xen-users@lists.xensource.com
> http://lists.xensource.com/xen-users
>
>
> End of Xen-users Digest, Vol 25, Issue 125
> ******************************************
>
_______________________________________________
Xen-users mailing list
Xen-users@lists.xensource.com
http://lists.xensource.com/xen-users