From mboxrd@z Thu Jan  1 00:00:00 1970
From: Anthony Liguori <anthony@codemonkey.ws>
Subject: Re: kvm-85: virtio-blk not working
Date: Thu, 23 Apr 2009 12:47:02 -0500
Message-ID: <49F0A996.6000203@codemonkey.ws>
References: <200904231043.05001.gerd.von.egidy@intra2net.com> <200904231110.47416.iggy@theiggy.com> <49F093BE.9030601@codemonkey.ws> <20090423162458.GQ5372@redhat.com>
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Cc: Brian Jackson <iggy@theiggy.com>,
	"Gerd v. Egidy" <gerd.von.egidy@intra2net.com>, kvm@vger.kernel.org
To: "Daniel P. Berrange" <berrange@redhat.com>
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Daniel P. Berrange wrote:
> On Thu, Apr 23, 2009 at 11:13:50AM -0500, Anthony Liguori wrote:
>   
>> Brian Jackson wrote:
>>     
>>> Your problem is that index's are per interface type, so both of your 
>>> drives should be index=0 since they are different interface types.
>>>  
>>>       
>> More specifically, with virtio-blk, you cannot have discontinuous 
>> indexes.   In other words, having index=0, index=1, index=2 is valid, 
>> but having index=1, index=2, index=4 is not.
>>     
>
> Is that restriction going to work with migration ?
>
> eg, you have a VM with 3 disks.  vda, vdb, vdc (index=0, index=1 and index=2).
> You then hot-unplug the 2nd disk, vdb (index=1).  Now migrate the guest to 
> another machine. I believe you now need to be able to start qemu on the target
> host with -incoming and index=0 and index=2, but no index=1 because that 
> disk was unplugged. So the indexes would be discontinuous now
>   

index doesn't have meaning with virtio-blk.

Each disk is dedicated to a PCI slot.  To support migration with 
hotplug, you need to specify the PCI bus address when creating the 
virtio-blk device.

Regards,

Anthony Liguori