cluster lock disk issues

[jithu_1]

Hello folks,

sorry if these have been answered before in this forum, I did some searching but couldn't really find the answers I was looking for.

am new to the MC/SG and hence these questions, please bear with me. thanx

1. it's a 2 node cluster, with one cluster lock vg/pv defined. active and passive node config.

2. if the active node has been up and running(pkgs) and cluster lock pv failed due to
harware failure(disk/path failure), would the cluster halt or panic, or we just see error mesg's in the log saying that cluster lock disk failed(I saw errors to this tune in this forum)..so am assuming as long as that active node is not shut/halted, the cluster/pkgs will keep running on active node.? lock disk is only used during cluster formation?

2. currently the single cluster lock pv is say /dev/dsk/c1t1d0 on both the active and passive nodes.
that is a cause of concern, as the access to that PV is via the same switch and FA(EMC). even though the PV has pvlink devices say for example c2t1d0 via a different switch(SAN) and FA(EMC) on both the nodes..so for best practice, in the cluster config file, for node1 use the lock disk to be /dev/dsk/c1t1d0 and for the node2 use /dev/dsk/c2t1d0. both point to the same physical lock disk via diff paths in the SAN.

3. Can we change the cluster lock PV device file on the node2 to /dev/dsk/c2t1d0..am assuming this requires shutting the cluster and then changing the config file and pusing the new changes??

please advise.
thanx in advance.
jithu

[melvyn burnard · Accepted solution]

If you have a cluster that is running, and the cluster lock disc fails, the cluster will continue to run, but will log Warning messages to syslog every 60 minutes (polling interval for cluster lock disc).
If, however, one node now dies/halts/fails, the surviving node HAS to be able to get the lock, and if this is not possible then theis node will TOC, as per design.

If the cluster lock disc is unavailable at cluster formation time, the cluster will still form, but with the same issue.

The ONLY time the cluster lock disc is NEEDED is to break an exact 50% quorum issue, i.e. EXACTLY 50% of the nodes die, leaving EXACTLY 50% surviving.

If you do wish to make the change you have mentioned, ensure that the new hardware path/device you are configuring is the primary path and not the Alternate Link, as this will appear to work, but will in fact not work under a failure condition.

HTH

[jithu_1]

have another follow-up question for this statement

"If the cluster lock disc is unavailable at cluster formation time, the cluster will still form, but with the same issue."

Does that mean, say if the cluster lock disk failed, the
node1 was shut/halted for
some reason, if I try bringing up node2(standby), it would still form cluster and bring up the packages etc even though the lock disk is un-available??

TIA
jithu

[melvyn burnard]

In a word, yes

[jithu_1]

Hello Melvin,

now am more confused:-)

1. according to the class notes/manual.
"without a cluster lock disk, the cluster would not be able to reform should one node fail, causing the entire cluster to go down"

in my case, the lock disk
was un-available, active node1
was shut/halted. tried to bring up the node2, it couldn't form the cluster and ceased cluster activities.

doesn't that mean, node2 needs
access to lock disk to bring up the packages etc..

TIA
jithu

[Christopher McCray_1]

It is required that you have a cluster lock disk for a two node cluster. This must be one of your shared drives accessible by both nodes. If this isn't possible, then cluster formation isn't possible. I would save your old cluster.ascii file by copying it to another file or cmgetconf command, and then do another cmquerycl to see what it gives you as to output.

Hope this helps

Chris

[melvyn burnard]

If the cluster has been configured and the binary generated, then if the cluster lock disc ismissing at initial cluster formation, then the cluster will form.
The case you mention is where the cluster was already runing, but when a node went down, then the other node needed to get the cluster lock disc, and failed, resulting in the remaining node going down.

Again I refer you to the fact that to create a new cluster, you must configure a cluster lock disc which must be available at the time of doing cmapplyconf. Once this is done, the cluster lock disc is ONLY used for decision making in the event of a tie, i.e. EXACTLY 50% of a cluster quorum remains.
Hence, if the cluster goes to start and the cluster lock disc is unavailable, the cluster will still form, itis only upon a failure that the cluster lock disc is actually needed.

[Kim Leong]

Hi Jithu,

I think Melvyn has explained really well on the concepts. I think you might be confused because of the terms being used.

Your post earlier reads :
1. according to the class notes/manual.
"without a cluster lock disk, the cluster would not be able to reform should one node fail, causing the entire cluster to go down"

and this is perfectly correct. The difference in terms might be causing the confusion. Here above it says the cluster will not be able to *REFORM*, and what it means is that if there is no cluster lock disk, and one of the nodes goes down ( leaving only the other running, and hence 50% of the cluster ) then the remaining node will TOC as well when it fails to get the cluster lock disk.

On the other hand, if you don't have a cluster lock disk - and you try to start a one node cluster, it will still *FORM* with or without the cluster lock disk.

Hope this helps.