Re: fibre channel tape drives accessed from multiple clusters

Colin Butcher wrote:
The FC protocol moves data between devices. That's all it's designed to do.

The way you set the infrastructure up determines which systems can see which devices. That's what "zoning" in the FC switches does (it's analogous to VLANs in a data network). In a SAN infrastructure where the zoning allows all HBAs to see all tape devices then you will have to implement some form of access control to ensure synchronised and serialised access to the available pool of tape drives.

Do beware of having Windows boxes capable of seeing the tape and robot devices as well as your VMS systems - the Windows removable storage service and the device drivers have a nasty habit of probing the tape and robot devices every so often, which can play havoc with operations in progress. It's easy enough to fix - just disable the relevant services and device drivers in the Windows boxes, or set up the zoning so that the Windows boxes cannot see the tape devices.

If you choose to have all your systems see all your storage devices or tape devices then you have to deal with the consequences by ensuring that you don't have multiple systems attempting to access the same device at the same time. It's not a problem that's unique to tapes. Disc storage arrays implement "device presentation" that describe which HBA WWIDs (systems) can access which available storage units (see the EVA Vdisk presentations or look at selective presentation in HSGs). Tapes don't implement device presentation as far as I'm aware - and while it might be a useful concept (presentations being a little easier to work with than SAN zoning) you'd still have to arbitrate access to the tapes if more than one system can see the tapes at any given instant in time.

In a VMS environment that's what ABS/MDMS does for you. ABS uses network communications to arbitrate access to the tape devices by having one (or more for redundancy) ABS servers allocate tape devices to client systems, the ABS servers manage the tapes and moving them around using the robot, then the ABS clients perform the backup functions directly to the tapes, then the ABS servers take care of the tape moving again.

Alternatively you should be able to write something pretty simple to synchronise access to the tape devices and robots, then used BACKUP as and when you need to. All you need to do is keep track of the tapes, robots and backup jobs across the separate clusters.

You could also control tape access by using SAN zoning in the SAN switches, thus restricting access from a single cluster to a single known set of tapes, however you'd have to change the SAN zoning if you needed to make those tapes available to other nodes / clusters.

However, why bother doing all that when you can buy the ABS server and client components? It's what I've done for the big systems I've been designing and building recently. ABS has been around for a good few years now. It works pretty well on the whole.

It's also worth reading the SAN design reference guide to understand SAN zoning and a few other things. See here: http://h20000.www2.hp.com/bizsupport/TechSupport/DocumentIndex.jsp?contentType=SupportManual&locale=en_US&docIndexId=179911&taskId=101&prodTypeId=12169&prodSeriesId=406734

It's not that difficult once you understand what's going on and why it all works as it does, then figure out what mechanisms you need to use to achieve what's needed.


With modern tape libraries you can do also do selective presentation of the tape drives (and the robotic). That will help somewhat. Then there is also a possibility to use different zoning for different needs. E.g. when you want to backup your VMS cluster you use one zone configuration and when you are done with that you change the zoning configuration to another one which will give access to the tape library for a winbloze cluster and so on. That kind of a zoning reconfiguration can be automated. There aren't many other means of synchronizing tape drive access in a heterogenous SAN on the SAN or OS level. Backup applications like ABS can keep track of tape drive access on the application level.


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Relevant Pages

  • Re: fibre channel tape drives accessed from multiple clusters
    ... In a SAN infrastructure where the zoning allows all HBAs to see all tape devices then you will have to implement some form of access control to ensure synchronised and serialised access to the available pool of tape drives. ... more for redundancy) ABS servers allocate tape devices to client systems, ...
    (comp.os.vms)
  • Re: fibre channel tape drives accessed from multiple clusters
    ... That's what "zoning" in the FC switches does (it's analogous ... In a SAN infrastructure where the zoning ... the available pool of tape drives. ... more for redundancy) ABS servers allocate tape devices to client systems, ...
    (comp.os.vms)
  • Re: fibre channel tape drives accessed from multiple clusters
    ... That's what "zoning" in the FC switches does (it's analogous to ... In a SAN infrastructure where the zoning allows ... available pool of tape drives. ... more for redundancy) ABS servers allocate tape devices to client systems, ...
    (comp.os.vms)
  • Re: fibre channel tape drives accessed from multiple clusters
    ... That's what "zoning" in the FC switches does (it's analogous to ... In a SAN infrastructure where the zoning allows ... available pool of tape drives. ... more for redundancy) ABS servers allocate tape devices to client systems, ...
    (comp.os.vms)
  • Re: fibre channel tape drives accessed from multiple clusters
    ... That's what "zoning" in the FC switches does (it's analogous to ... available pool of tape drives. ... In a VMS environment that's what ABS/MDMS does for you. ... ABS uses network ...
    (comp.os.vms)