Dual FC connection in MSL 2024 & MSL 4048

[Leonard Thng]

Hi..

I've got 2 SAN switch and i need to connect up a tape library to these 2 switches for redundancy / failover. I've seen the MSL 2024 & 4048 guides and there's a dual FC ports available. Will i be able to perform such redundancy / failover in such an environment mentioned above??

[shIVinator.]

I have never worked with the 2024 or 4048 but I have with the 6000 series. If the same holds true then when you have multiple fiber cables coming out of a library each SCSI to Fibre bridge each fiber cable will handle its own drive(s).

This is not a problem if you have two backup servers each with its own drive(s) but if you put one set of drive(s) on one fabric and the other two on the other fabric you could have problems with your backup if a failure occurs. If you have a fabric go down then there is a chance that your backup server could have the tape drive mappings messed up, causing you headaches.

You mentioned that it is a dual FC port card. If it is in fact a dual port card going to the same SCSI to Fibre bridge then disregard what I said above. The only thing I would look out for is how will the server react to the same tape drive showing up twice (once for each path). I don't believe that MPIO or secure path does anything for tape.

As an installer I would always put both fiber cables into the same fabric (for the MSL6030).

Duane

[Curtis Ballard]

Yes the 2024 and 4048 has two ports on each FC tape drive and can be used in that configuration if you have software that understands multi-ported devices or if you zone out one link and re-zone in case of failure.

Many backup applications do not understand multi-ported tape drives and will report the different ports as different drives so you will see two of everything and then it is an administrative headache. You need software that understands multi-porting and will detect the same ID on two ports then select the preferred port.

[Leonard Thng]

Hi Curtis,

The failover from the 1st port to the 2nd is via manual way or is there an auto failover?

Is there any software that can be configured to auto failover the FC path??

[Curtis Ballard]

For automatic failover, the failover has to be controlled by your backup application so check with your backup application provider and see if they support dual paths with failover. Applications that support dual paths typically will automatically resolve them to a single device and pick one path as preferred. When an error occurs the backup in progress will usually be aborted and fail but then the application will switch which path is preferred and the next command to that drive will switch to the failover path.

Manual failover is more difficult. There is no software that will disable one of the ports so that applications only see one port but you can simulate that behavior with zoning in your SAN switches. If you configure dual paths then pick the preferred path and then configure zoning in the second path so that the backup host does not have access to the tape drive then your host will only see on port. When there is a problem on the preferred path you can log into your switches and change the zoning to disable the primary path and enable the secondary path. Kind of awkward but it creates the same effect as manual path failover.