RE: [Xen-users] Shared SAN disk LUN between 2 servers and migrationproblem

[Pekka.Panula@xxxxxxxx]

xen-users-bounces@xxxxxxxxxxxxxxxxxxx wrote on 20.10.2008
20:37:57:

> "Simon Talbot" <simont@xxxxxxxxx> 
> Sent by: xen-users-bounces@xxxxxxxxxxxxxxxxxxx
> 
> 20.10.2008 20:39
> 
> To
> 
> "John Madden" <jmadden@xxxxxxxxxxx>, <xen-users@xxxxxxxxxxxxxxxxxxx>
> 
> cc
> 
> Pekka.Panula@xxxxxxxx, Ferenc Wagner <wferi@xxxxxxx>
> 
> Subject
> 
> RE: [Xen-users] Shared SAN disk LUN between 2 servers and migrationproblem
> 
> We have a 6 server Xen cluster, with shared SAN storage (directly
> presenting LUNs to the host OSs). Live migration works well for both
PV
> and HVM domains, the only times that we have observed file system
> corruption is when heartbeat has mistakenly brought the same VM up
on
> two machines. 
> 
> Apart from that we had a test harness performing around 10,000 live
> migrations randomly around the 6 server cluster without a single
> incident, the domain ran perfectly throughout the test.
> 
> Once scenario I could imagine problems in however, is if your OS/HBA
is
> performing caching on the write operations to the SAN, so say for
> example you have the domain started on Server A and heavy IO is taking
> place. You live migrate to Server B and dirty data is still in the
cache
> of Server A being written to the SAN. Server B then starts running
and
> continues the heavy writes before Server A is fully flushed, this
then
> potentially leads to the two servers effectively both fighting over
the
> same device for a short period of time until Server A's cache is fully
> flushed.
> 
> I must stress that we have **NOT** experienced this problem and in
> general the Host OS cache is fully flushed as part of the Live
> Migration, but it could be a problem in some situations where something
> in the data path is performing caching that the Host OS/Xen has no
> knowledge of.
> 
> What Servers/SAN/HBAs etc. are you using?
> 
> Simon
> 
> Simon Talbot MEng, ACGI 
> (Chief Engineer) 
> Tel: 020 3161 6001
> Fax: 020 3161 6011

I tested also with paravirtualized CentOS 5.2 32-bit
and i did not got any corruption during 7-zip or with zip. I did migrate
atleast 4 times during compression and then i did verify compressed file
and they all say it was ok.

I did get corrupted with Windows 2003 standard server,
with HVM drivers and with GPLPV drivers. Compression program was 7-zip
latest beta i think, maybe 7-zip does not like virtualized servers. 

Storage is IBM DS-series and Xen servers are on BladeCenter
H HS21 cards, so HBA is "QLogic Corp. ISP2422-based 4Gb Fibre Channel
to PCI-X HBA (rev 02)", driver: 8.02.00-k5-rhel5.2-04

Anyone else running Xen with similar system and does
your HVM Windows DomU migrate without filesystem corruptions?

BTW: I did test also Xen 3.3.0 but interestingly you
cant migrate it with 3.2.1 Xen, is this bug or should it work? 

Terveisin/Regards,
   Pekka Panula, Net Servant Oy
_______________________________________________
Xen-users mailing list
Xen-users@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-users