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Date: Fri, 14 Feb 2014 11:58:56 +0100
From: Michal Privoznik <mprivozn@redhat.com>
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Subject: Re: [Qemu-devel] [libvirt-users] Adjust disk image migration (NBD)
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To: Joaquim Barrera <jbarrera@ac.upc.edu>, Libvirt Users <libvirt-users@redhat.com>
Cc: qemu-devel <qemu-devel@nongnu.org>

On 14.02.2014 10:40, Joaquim Barrera wrote:
> Hi all,
> 
> As I am doing some tests with qemu, I realized that the way it does 
> 'migrate -i tcp:DEST:444' is not the same as 'libvirt migrate 
> --copy-storage-inc'. Basically qemu uses the same stream as RAM 
> migration and libvirt takes advantage of NBD transfer.
> 
> With virsh migrate-setspeed I observed that one can only control the 
> transfer throughput of RAM, but not disk synchronization. At least this 
> is what I can see in bmon when doing a migration with incremental copy.
> 
> The question is: Am I missing something or it is not implemented?
> 
> Thank you guys!
> 

I think this is actually a qemu bug. Libvirt passes the correct values:


2014-02-14 10:52:08.010+0000: 27701: debug : qemuMonitorIOWrite:504 : QEMU_MONITOR_IO_WRITE: mon=0x7f06cc00ea20 buf={"execute":"drive-mirror","arguments":{"device":"drive-virtio-disk0","target":"nbd:masina:49153:exportname=drive-virtio-disk0","speed":1048576,"sync":"full","mode":"existing"},"id":"libvirt-15"}


...

2014-02-14 10:53:51.169+0000: 27701: debug : qemuMonitorIOWrite:504 : QEMU_MONITOR_IO_WRITE: mon=0x7f06cc00ea20 buf={"execute":"migrate_set_speed","arguments":{"value":1048576},"id":"libvirt-221"}


2014-02-14 10:53:51.204+0000: 27701: debug : qemuMonitorIOWrite:504 : QEMU_MONITOR_IO_WRITE: mon=0x7f06cc00ea20 buf={"execute":"migrate","arguments":{"detach":true,"blk":false,"inc":false,"uri":"fd:migrate"},"id":"libvirt-223"}


However I observe what you do - disk migration is not shaped, while internal state is.


Michal