Xen users - May 2006 - relocation time about 20sec? and yours?

Hi List,

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
Links and the storrage is connected via iSCSI. The iSCSI volumes have a
performance about 20-40MByte/s. Servers A is a 2x2GHz Xeon with 4GB Ram
and Server B is a 1.8GHz AMD with 2GB Ram. 

The documentation states about some 60-300msec, so my qestion is:
How long takes it on your Servers to migrate a DomU from A to B, what kind of
storrage do you use. 
And certainly how can i fasten this process?

Any suggestion is appreciated.

regards Martin
-- 
----------------------------------------------------------------
  Does the Enterprise use DOS v 2356.0?
----------------------------------------------------------------

_______________________________________________
Xen-users mailing list
Xen-users@lists.xensource.com
http://lists.xensource.com/xen-users

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


_______________________________________________
Xen-users mailing list
Xen-users@lists.xensource.com
http://lists.xensource.com/xen-users

> 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
> Links and the storrage is connected via iSCSI. The iSCSI volumes have a
> performance about 20-40MByte/s. Servers A is a 2x2GHz Xeon with 4GB Ram
> and Server B is a 1.8GHz AMD with 2GB Ram.
>
> The documentation states about some 60-300msec, so my qestion is:
That''s the downtime to complete the migration.  In live migration, you
still
need to spend some time (20secs sounds reasonable) precopying memory over.  
The domain is only actually stopped for 60-300msecs but the whole process 
takes longer (nb. make sure you''re passing the live migration flag - I
think
it''s -l or --live)
> How long takes it on your Servers to migrate a DomU from A to B, what kind
> of storrage do you use.
We''ve used iSCSI, I think.  NBD should work fine, a SAN should also
give good
performance.

You should be able to use a local block device and sync it up with DRBD, in 
principle, but the last I heard was that the available DRBD release made that 
hard.  I know this was a problem that would be fixed by the multi-writer DRBD 
enhancements.
> And certainly how can i fasten this process?
>
You could balloon the domain down before migrating it to reduce the precopying 
time, but this will cost performance and so is probably not worth it.
> Any suggestion is appreciated.
HTH,
Mark

-- 
Dave: Just a question. What use is a unicyle with no seat?  And no pedals!
Mark: To answer a question with a question: What use is a skateboard?
Dave: Skateboards have wheels.
Mark: My wheel has a wheel!

_______________________________________________
Xen-users mailing list
Xen-users@lists.xensource.com
http://lists.xensource.com/xen-users

Hi,
> you''re comparing apples and oranges.  the 60-300msec figure is
downtime, while
> your 20sec seems to be the whole migration time.
no, the 20sec are the real downtime. I am pinging the DomU while
migrating (yes, live migration) and i lost about 20 icmp replies. So it
is not the whole process of copying memory 3 or 4 times and al the other
stuff. 
This 20 secs while the DomU is not responding to network packets is
downtime, for me. Also my ssh connection to the host is lost.
> > 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
FC and NBD over Gigabit Ethernet should be the same as iSCSI. 

regards Martin

-- 
----------------------------------------------------------------
  Does the Enterprise use DOS v 2356.0?
----------------------------------------------------------------

_______________________________________________
Xen-users mailing list
Xen-users@lists.xensource.com
http://lists.xensource.com/xen-users