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Re: [Xen-devel] xm block-configure


Here's the sequence of events.  Provision LVM for a VM.  This creates a DM device.  It has a certain size.  Boot the VM on it.

Later on, customers wants more space.  We expand the logical volume with LVM, which does some cleverness with the DM device to cause it to grow bigger.  This is pretty much plain-jane LVM up to this point.

When we check the size of the block device from outside the VM, it shows the new size.  From within, it shows the old, smaller size.  In the olden days, you could do "xm block-configure ...." to cause the VM to pick up the changes.  That hasn't worked for me for ages (and digging in the code turned up some interesting comments indicating that it may have not been re-implemented during a rewrite).

On Apr 13, 2008, at 8:58 AM, Mark Williamson wrote:
Our business currently provides literally thousands of VMs with
filesystems via blkback / blkfront.

Wow!  Cool :-)

For security purposes, it's
absolutely critical that we keep LVM outside of the VMs.

OK.  I generally recommend keeping LVM outside VMs anyhow, to ease

What is the
feasibility of getting block-configure to actually update the DomUs
concept of the disk of a block device device?

It hasn't worked for us for quite a while.

I don't quite understand what you're trying to do?  Could you please provide a
little more detail?

Is the idea just to make the resizing of LVM volumes visible to the guest?  
I'm not sure exactly why this would be broken but I can imagine it might have
been.  It'd certainly be a useful feature to have back.


Push Me Pull You - Distributed SCM tool (http://www.cl.cam.ac.uk/~maw48/pmpu/)

Jayson Vantuyl
Systems Architect
1 866 518 9275 ext 204

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