ServiceGuard and JBOD

[Woo Kim Chye]

I want to install ServiceGuard on 2 K-class server. I have a rack full of JBOD disks.
Is it possible to configure the SC using JBOD. If yes, how do I connect the servers to the JBOD disks such that when 1 node fail, the other node can still access the disk.
The manual mentioned that I need at least 2 JBOD, is this true??
Thanks.

[Sridhar Bhaskarla]

What is the JBOD you have?. If it is like SC10
you can use it for Service Guard. Basically it should be dual-hosted.

The SCSI IDs of the cards on the hosts should not be equal. You also need to use SCSI inline terminators at both the ends on the hosts to maintain the termination in case of a system failure.

-Sri

[linuxfan]

Hi Woo,

Yes it is very much possible to set up MC-SG on 2 K-class servers accessing JBODs.
Do you have the A3312 arrays with the hot-swappable jamaica drives ? Actually irrespectly whats more important in the MC-SG is you are trying to set up a very HA(High Available) machines which includes redundant power, network connections, I/O paths, redundant access to the (shared) disks, hearbeat connections between the nodes (serial/ethernet). Each of these redundancy is from each host(node) in the cluster.
Actually the document Managing MC-Service Guard ( http://docs.hp.com/hpux/pdf/B3936-90045.pdf)
will clear out some of your doubts.

Regarding your question do we need atlest 2 JBOD, no you do not need 2 JBODs, what you definitely need to set up a High available set up is atleast two SCSI-connections from each server to the JBODs. Pay particular attention to the SCSI ids(targets) when you share disks on the same bus.

Hope that helps
-I am RU

[linuxfan]

Hi,

Just had another thing to add, the reason they specify two JBODs is so that disks on the first JBOD have mirrors on second JBOD. So ideally it is always better to have two JBODs with redundant connection to each node from each JBOD.

-Regards
I am RU

[Woo Kim Chye]

Hi Ramesh,
Yup, the JBOD I have is A3312 arrays with the ho-swappable jamaica drives.

Do I need to have the inline terminators as mentioned by Sridhar??

You mentioned that at least 2 SCSI connections from each server to the JBOD, is it means that I got to have 2 SCSI card on each server and a connection from each card to the JBOD?
Thanks.

[linuxfan]

Hi,

The inline termination cable (C2980A) is recommended because it moves the SCSI termination form the SCSI card to the cable.

If you don't use this cable then none of the JBODs can be shutdown/powered down but if you use this cable then the termination ends at the inline terminator itself so it makes the set up highly available.

Would MC-SG work without this cable? Yes it would but again like i said it would mean all the devices have to be up and there can be no disruption in the SCSI chain anywhere.


-HTH
I am RU

[Sridhar Bhaskarla · Accepted solution]

Woo,

We configure MC/Service Guard for the high availability of the applications. MC/Service Guard will be fine as long as both the systems are up and running. For JBOD systems, inline terminators are required. Let's say one of the systems in the cluster goes down then the SCSI chain loses termination and the other system will also hang/crash.

So, this is a safety feature that needs to be dealt with.

-Sri

[Woo Kim Chye]

If I have a configuration as shown below. Is that means that the other node will hang/crash when one of the node is down without the inline terminator??

Is there a way to make the disks still accessible by the standby node when the active node is down??

Thanks.

[linuxfan]

Hi Woo,

Ideally you would want two scsi-connections from each node to each JBOD.

Yes you would need inline terminators from the the nodes, look at page 176 in the document http://docs.hp.com/hpux/pdf/B3936-90024.pdf
It will give you more information as to how/when to use the inline terminators.
-HTH
Ramesh

[Sridhar Bhaskarla]

Here we lack in having alternate links but mirror disk will take care of it.

Yet, your system will hang if the other system goes down because you are losing the termination for both the paths. Inline terminators are required.

-Sri