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Re: [Xen-users] problem in xen guest

To: Naveed Iqbal <naveed00786@xxxxxxxxxxx>
Subject: Re: [Xen-users] problem in xen guest
From: Thomas Goirand <thomas@xxxxxxxxxx>
Date: Mon, 16 Feb 2009 17:19:21 +0800
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Naveed Iqbal wrote:
> How many xen guest can run parallel?we have Fedora core 8 host(dom0) and
> 9 Fedora caore 8 xen guest(domU) but only 8 guest run parallel when we
> try to run 9th guest then error comes which is
>  return self.xd.domain_start(self.dom.getName(), paused)
>   File "/usr/lib/python2.5/site-packages/xen/xend/XendDomain.py", line
> 999, in domain_start
>     dominfo.waitForDevices()
>   File "/usr/lib/python2.5/site-packages/xen/xend/XendDomainInfo.py",
> line 546, in waitForDevices
>     self.getDeviceController(devclass).waitForDevices()
>   File
> "/usr/lib/python2.5/site-packages/xen/xend/server/DevController.py",
> line 149, in waitForDevices
>     return map(self.waitForDevice, self.deviceIDs())
>   File
> "/usr/lib/python2.5/site-packages/xen/xend/server/DevController.py",
> line 174, in waitForDevice
>     "%s" % (devid, self.deviceClass, err))
> VmError: Device 51712 (vbd) could not be connected. Failed to find an
> unused loop device
> so how many xen guest(domU) can run parallel?There is any limitations?

The limitation that you are seeing here is NOT the number of domU, but
the number of LOOPBACK devices. To fix this, you should set the kernel
option to allow to use more loopback devices.

By the way, using loopback file devices is a very bad idea, it's a lot
slower than using LVM. Look at how to setup LVM and you will have no
limitation, and it will be a lot faster.


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