Identifying Used Shared Disk in a Cluster

[Chin Jin Kiat]

Hi,

Disk device files may differ across nodes for the same physical device on a clustered solution. What is a reliable was to determine that c1t2d3@serverA and cXtYdZ@serverB are referring to the same physical device without having the need to understand the disk technology in use and physically mapping/correlating the devices?

Regards,
JinKiat

[John Poff]

Hi,

You really can't get away from understanding the disk technology and disk mapping in a cluster situation, but I guess one of the easiest ways to look at it from the volume group level is to look at the /etc/lvmtab file and compare entries for the same volume groups between nodes.

It looks like the newer disk array software offerings are getting more sophisticated about keeping track of disks and reporting which are actually in use, but you still need to understand what is being used.

JP

[Rajeev Shukla]

See in a clustered environment its always best to have a synced /etc/lvmtab file which means..
1. export the volume group in shared mode using "-s" option and import that volume group in all machines in the cluster this will create a common lvmtab file and by looking at a file on one node itself you can say which disks are free also you can create a map of disk as seen from different system.
Let me know if you need more info as how to do this.

Cheers
Rajeev

[RAC_1]

/etc/lvmtab is the file you shoud look at.

also the diskinfo from different nodes can throw light on this, but not recomanded.

[Chin Jin Kiat]

*nod*

Thanks for the reply.

We're trying to formulate some easy means for the task to be performed by 1st level support. I do not expected them to be able to understand disk technology in-depth hence my attempt to shy away from lvmtab.

I was hoping that there is a way to uniquely identify a disk in a cluster - Some sort of physical disk or volume ID - Any idea?

[Sridhar Bhaskarla]

Hi,

If your backend is EMC or XP, there are tools available that can help you identify.

EMC - inq
XP - xpinfo

Check with your EMC and HP vendors to supply you with these tools.

If you don't have them, then you have to map. If they are shared, then it is easy to map because only the controller (cx) numbers change.

So, if the disk is c1t2d3 on Server A, then you just need to find the corresponding cx and it would be cxt2d3.

-Sri

[Jochen Heuer]

Hi,

there exists a tool called 'cmpdisks' which does exactly what you want. Check with your local Response Centre. They should be able to provide it to you.

Jochen