MSA1000 Redundancy

[Dustin Loftis]

Hello,

I have an MSA1000 w/ redundant controllers and two switch modules in the back.

I'm wondering if a server connected to just ONE of the two switch modules can communicate with both controllers... In other words, if a server is connected to ONLY the primary switch, it can see the primary controller just fine... but if the primary controller fails, will that server be able to see the redundant controller when it takes over?

Thanks!

[Uwe Zessin]

Dustin,
a controller has only one direct connection to the embedded fibre channel switch. A host with only one connection will not have access to the other controller, because interconnecting both switches is not supported.

The situation can even be worse, because the MSA1000 currently uses an active/standby controller configuration. A host with connections to both controllers will see two paths to the LUNs, but can only do I/O to the active controller.

If one host causes a controller failover (e.g. due to a failure on the active path) it means that ALL of the LUNs will failover. A server with only one connection will loose access to his data!

[Greg Carlson]

Dustin,

To achieve redundancy, you need to have a second HBA connected to the second controller as Uwe mentioned. You must also purchase Secure Path to achieve failover functionality without having to down the MSA1000.

If you are running MS, you need this part number:
HP StorageWorks Secure Path v4.0C for Windows Workgroup Edition 213076-B26

Regards,
Greg

[Dustin Loftis]

Thank you both for your responses.

Assuming I don't use the 2nd controller or a 2nd HBA, just a single HBA with a single controller, is there any need for SecurePath?

[Greg Carlson]

Dustin,

If you only have a single path, single HBA or single controller on the MSA. Then there would be no need for SecurePath.

Regards,
Greg

[Imel Rautenbach]

Hi guys,

I have been through this pain recently and finally decided to go with dual HBAs & Securepath on all machines (2 windows & 2 Linux, all connected to the same MSA1000).

Originally we wanted some machines connected to one switch and others to the other switch. This way we could loose one half if the switch failed.
Sadly we only realised later that the MSa operates in active/passive mode, so only one switch is active at any time.

Apaprently HP is planning on bringing out a firmware update that will allow the MSA1000 to operate in active/active mode, thereby allowing the above scenario as well asload balancing?

Regards
Imel

[Uwe Zessin]

The fibre channel switch is fully active all the time and the standby controller presents the LUNs - otherwise the multipath software would not be aware that there is an alternate path.

I would wait until the active/active mode really materializes (most MSA1000 announcements I have seen were delayed) and then look how this is implemented. Historically, controllers from the DEC/Compaq StorageWorks line do not allow I/O to a single LUN via two controllers, if that is what you call 'load balancing'.

If you have one Linux system connected to a redundant MSA1000, then ALL other servers must be connected redundant, too. The reason is that a Linux server can cause a controller failover during boot.

[Imel Rautenbach]

In our case we will have four machines (2 windows, 2 linux) connected vua dual hba's & securepath, but we will also have an additonal 3 linux boxes connected via single hba's to only one (the active) controller (no securepath).

If the active controller fails we will loose connectivity fro mthe tree single HBA servers, but securepath will sort the rest.

I presume this setup should work ok, as long as we are willing to take the downtime on the single HBA servers?

[Uwe Zessin]

Imel,
it is my understanding that any of the Linux servers with redundant connectivity can cause a failover during boot. If you can live with this and the fact that this is an unsupported configuration - fine with me ;-)

[Cass Witkowski]

We are looking at using the MSA1000 with OpenVMS machines but because of slot limitations we can only have one HBA.

So why can't the switches on the back of the MSA1000 have a link between the two?

[Doug de Werd]

It's not the switches that is the issue, it's the fact the MSA1000 controllers are active/passive (the switches are actually both active). So even if you connect the 2 switches, it won't do you any good because the 2nd controller is not active. SecurePath is required to switch from the active controller to the standby one.

Thanks,
Doug

[Cass Witkowski]

In my case I'm running OpenVMS which has multi-path capability built in

[Uwe Zessin]

I have never seen a configuration example that allows one fibre channel adapter to have access to both controllers, but you could try it out and see if the MSA1000 allows two connections on the controllers with the same WWN.