[Xen-users] Re: DomU Disk-Intense Operations kill Xen-Server?

[bigfoot29@xxxxxxxxxxxxxxxxxxxxxx]

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@xxxxxxxxxxxx>
> Subject: RE: [Xen-users] How can I create another privileged domian?
> To: "Prabhakar Chaganti" <pchaganti@xxxxxxxxx>
> Cc: xen-users@xxxxxxxxxxxxxxxxxxx
> Message-ID:
>       
> <BA9C9E8D6DE58F43B85F33C5FC1E1F260165A925@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx>
>
> 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@xxxxxxxxx]
> Sent: Monday, March 19, 2007 10:03 PM
> To: Ashit Kumar
> Cc: xen-users@xxxxxxxxxxxxxxxxxxx
> 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@xxxxxxxxxxxx
> <mailto:Ashit_Kumar@xxxxxxxxxxxx> > 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
>
>
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