Forwarding a mail from Kalyani on this :-



From: Kalyani Sundaralingam

Sent: Monday, April 02, 2007 12:26 PM


Cc: Eric Hennessey; Kalyani Sundaralingam

Subject: FW: Veritas-ha Digest, Vol 12, Issue 1


Hi Pavel,

One general comment: If both the nodes of the cluster are lpars on the
same frame, the frame itself becomes a single point of failure. Hence,
this is not a recommended configuration from VCS' standpoint. 

The recommended configuration for a 2-node VCS cluster in a VIO env is
to have both nodes on different frames, each serviced by a VIO server
local to that frame. Consider p1 and p2 as two frames; vio11 is on p1
and vio21 is on p2; n11 is on p1 and n21 is on p2. n11 and n21 are the
2-nodes in the cluster. There can be other systems local to each frame
that use the same VIO server for virtualizing storage and network
access. Those other systems may or may not be in the same cluster. The
main issue here is with the way the SCSI reservations are handled by LVM
on the lpar and the VIO.

In this configuration, the mkvdev command, when invoked on the first vio
server (vio11) places a reservation on the disk on behalf of vio11. Now,

n11 will be able to see the virtual disk. For the LVMVG agent to work,
n21 should also be able to see the same disk (in AVAILABLE state) and
that's where the problem comes in. In order to create the virtual target
disk for n21's use, you first need to run the mkvdev command from vio21
and this command will fail. It fails because of the reservation placed
by vio11. As a result, n21 will not be able to see the disk. The LVMVG
agent will not work in this configuration, as a result. We're working
with IBM to solve this issue so that the reservations are placed on the
disk by the client lpars and not by the vio server.

Getting back to your configuration, please note again that the
reservations initiated by LVM on the client lpars are actually placed on
the VIO server and do not make it to the array. It is only the vio
server (mkvdev) that places the reservations on the disk. The agent
might work but LVMVG is not tested in this environment since the
configuration is not a recommended one. Also, note that the single vio
server itself is a SPOF in your configuration. And if you were to change
the config to have 2 vio servers on the same frame, then the reservation
issue (from the previous para) should show up there as well.

Hope this helps. Let me know if you've any questions. BTW, what version
of the VIO server are you using?




[mailto:[EMAIL PROTECTED] On Behalf Of Pavel A
Sent: Monday, April 02, 2007 7:13 PM
Subject: [Veritas-ha] LVMVG agent does work with VIO ! ! !

Hello all! 

My  last post was a question about Symantec  support of LVMVG agent in
VIO configuration. It seems to me nobody could answer my question... 
So I decided to check it out myself. I installed VCS Cluster 5 MP1 for
AIX on my 570 server with two LPARs and two VIO-s. I  used only one VIO
in my configuration. 
 One disk was shared by VIO for  two LPAR-s.  The LVM group was created
and clustered. Everything was quite right! No problems with switching
over of the LVM group from one LPAR to another. 
 So I'd like very much  to get any comments from Symantec people ! 

  Regards, Pavel 
Veritas-ha maillist  -

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