Re: [Xen-users] relocation time about 20sec? and yours?

[Javier Guerra <javier@xxxxxxxxxxx>]

On Friday 19 May 2006 12:07 pm, Martin Hierling wrote:
> i have running xen-3.0.2 and my migration time for DomU from Server A to
> Server B is about 20sec. The Servers A and B are connected over 1GBit/s
....
> The documentation states about some 60-300msec, so my qestion is:

you're comparing apples and oranges.  the 60-300msec figure is downtime, while 
your 20sec seems to be the whole migration time.

live migration is a complex operation, but most of it is done with the domU 
process still running, so it's not downtime (yet).

1) first it does some setup
2) then the whole RAM is copied (with some bandwith limitation, so the network 
isn't saturated).
3) any RAM pages that had been modified by the still running domU get copied 
again. 
4) repeat step 3 a few times, until Xen realizes it's not advancing much. 
5) suspend the domU, copy any remaining modified pages and resume the domU at 
the new host
6) send a few packets so any ethernet switch updates its MAC table

only steps 5-6 can be considered as downtime, it's the only time the domU 
wasn't running. the whole 1-6 time is a lot longer, but less impacting to a 
server availability

> How long takes it on your Servers to migrate a DomU from A to B, what kind
> of storrage do you use.

i think those 60-300msec tests were done both with FC and NBD

-- 
Javier

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