[prev in list] [next in list] [prev in thread] [next in thread] 

List:       evms-devel
Subject:    Re: [Evms-devel] [Evms-cluster] Access to EVMS volumes with CSM
From:       Thomas Guyot-Sionnest <thomas () zango ! com>
Date:       2008-04-29 15:51:54
Message-ID: 4817441A.1020105 () zango ! com
[Download RAW message or body]

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

Steve Dobbelstein wrote:
| Maximilian Wilhelm <max@rfc2324.org> wrote on 04/25/2008 01:15:48 PM:
|
|  > Hi!
|  >
|  > I've set up a Xen-Cluster with two nodes sharing some SAN storage.
|  >
|  > I decided to use EVMS to cut on of the LUNs into pieces for the DomU
|  > storage. So I put a CSM on the LUN devices, and some LVM stuff in
|  > there.
|  >
|  > If I now reboot/poweroff one node for any reason, the /dev/evms/...
|  > devices managent by CSM on the running node disappear, which is quite
|  > bad as I cannot start Xen DomUs when one node failed.
|  >
|  > Is this intentional or can I do anything about that?
|  >
|  > I can't imagine any reason for this behaviour and would realy like to
|  > be able to use the volumes if only one node is alive.
|  >
|  > Ciao
|  > Max
|  > --
|  >    Follow the white penguin.
|
| Hi, Max.
|
| The EVMS CSM will not display any shared storage on a node if that node
| is not in the membership of the cluster.  The reason is that if the node
| is not in the membership then the CSM cannot guarantee that the node can
| safely access the shared storage.
|
| Last I heard it was still undecided if a single node in a two node
| cluster can declare that it is part of the membership of the cluster.
|  All that the node can determine is that it cannot talk to the other
| node.  It doesn't know if it is the only one alive or if it lost its
| connection to the other node.  If the other node is alive, which one is
| in the membership and which one is not?  If both nodes are up but cannot
| talk to each other, neither one can declare that it is the one in the
| membership and that the other node isn't.  The typical way to handle the
| scenario is to have the node declare itself as not being in the
| membership.  This is the safe solution.  I have heard that there are
| some implementations or scenarios that allow one node to have then
| membership, but I don't recall the specifics.
|
| If you want to check if your node is in the membership, run "evmsccm
| -l".  The evmsccm command is used by EVMS to determine if a node is in
| the membership.  The "-l" switch says to list the nodes in the membership.

I'm using EVMS CSM's in a 2-node Linux-HA cluster (Linux-HA v2.x with v1
config) and I don't have any problem with single node. If one node
gracefully quits (/etc/init.d/heartbeat shutdown) the other node keeps
membership. If communication breaks the other node gets gets STONITH'ed
instead (using both serial & udp for communication).

Also if I start a node and it can't communicate with the other one it
will STONITH it before taking resources. For that reason I don't start
heartbeat on bootup to avoid possibility of broken communication causing
nodes to kill each other in a round-robin way :)

- --
Thomas
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.7 (MingW32)
Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org

iD8DBQFIF0Qa6dZ+Kt5BchYRAhHkAKC02Tcij0G1HkqseKymi/GvWN96+QCgwx/W
w5CFNK+pbkMNrTd0KjJOlw0=
=MhTk
-----END PGP SIGNATURE-----

-------------------------------------------------------------------------
This SF.net email is sponsored by the 2008 JavaOne(SM) Conference 
Don't miss this year's exciting event. There's still time to save $100. 
Use priority code J8TL2D2. 
http://ad.doubleclick.net/clk;198757673;13503038;p?http://java.sun.com/javaone
_______________________________________________
Evms-devel mailing list
Evms-devel@lists.sourceforge.net
To subscribe/unsubscribe, please visit:
https://lists.sourceforge.net/lists/listinfo/evms-devel
[prev in list] [next in list] [prev in thread] [next in thread]