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HP OpenVMS Systemsask the wizard |
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The Question is: I have 2 Alpha 2100 on a CI cluster and a TA90 Tape drive on an HSC. There is another standalone AlphaStation 255 which needs to have access to the TA90 tape drive. I know that the only way to do this is by adding the AlphaStation to the existing cluster but this is not possible since an AlphaStation is not supported under a CI cluster. The only option I have is to go for a LAN(ETHERNET) based Cluster with the AlphaStation 255 configured as a satellite client. My question is, how can I make this configura tion on a DEC TCP/IP network? I've checked the VMScluster manual and I cannot find any discussion about this. I would appreciate your assistance. The Answer is : An OpenVMS Cluster operates using a protocol known as System Communication Services (SCS), and SCS can operate over a variety of communications ports. Available ports include CI, Ethernet, DSSI, Memory Channel, FDDI, Galaxy shared memory, etc. Specific cluster interconnects have specific capabilities and prerequisites. SCS is compliant with Ethernet and IEEE 802.3 requirements and can thus share an Ethernet or 802.3 network with other protocols, such as DECnet, IP, and LAT. SCS does NOT operate over DECnet nor IP protocols, it shares the network with these protocols. An OpenVMS Cluster can operate (standalone) when there are no cluster interconnects present, and can also obviously operate when there are one or more cluster interconnects present. The central requirement of interconnections is that every node must have a direct connection to every other node -- this is certainly easiest with a uniform connection to a broadcast medium, but it can also be met through other means. (ie: Connecting all members to the same Ethernet, 802.3, CI, or FDDI medium is the easiest way to meet the requirement for total connectivity, but many other configurations are also equally valid. For example, total connectivity can be achieved with three hosts when each node has two DSSI buses, each shared with one other node -- this particular configuration is often drawn as a triangle with the hosts represented as the vertices and the three DSSI busses present as the legs.) An OpenVMS Cluster must have at least one system disk. Multiple system disks are permissible, and at least two system disks are required for mixed-architecture cluster configurations -- one for OpenVMS VAX and one for OpenVMS Alpha. An individual OpenVMS Cluster member can have a local or direct access to the system disk, or it can be configured as a satellite of another member. Systems with local or direct access operate the same as standalone OpenVMS nodes. Satellite systems differ in the initial system bootstrap -- the system console requests a download using the maintenance and operations protocol (MOP). MOP is available as part of DECnet Phase IV, DECnet-Plus, and (in OpenVMS V6.2 and later) in the OpenVMS LANCP utility. Once the satellite download request is made and then serviced, all subsequent OpenVMS Cluster traffic uses SCS protocols. An OpenVMS Cluster includes a mechansim known as the connection manager, and this connection manager is what prevents user and system data corruptions that can result from a situation known as "partitioning" -- partitioning is a situation where systems modify resources without the necessary coordination. Extensive information on the specifics of the connection manager and on quorum is included in the OpenVMS Frequently Asked Questions (FAQ), in the section of the FAQ describing the appropriate settings of the SYSGEN parameters VOTES and EXPECTED_VOTES. Typically only members with direct access to a system disk are configured as voting members of the cluster. While satellites can vote, they cannot bootstrap to contribute a vote when the cluster is forming, or when the cluster is in a state known as a "user data integrity interlock" or "quorum hang". In your specific case, the CI nodes can be configured to use the Ethernet or IEEE 802.3 network as an additional cluster communications port, and the AlphaStation 255 can be configured with the same cluster group number and cluster password. The values of the SYSGEN parameters VOTES and EXPECTED_VOTES will need to be set per the description in the OpenVMS FAQ, and the SCSNODE and SCSSYSTEMID parameter values will also need to be set per the OpenVMS Cluster documentation. (SCSNODE is typically set to six or fewer alphanumeric characters, usually the same as the nodename. SCSSYSTEMID is set to a unique value, usually to the DECnet Phase IV host address (when DECnet Phase IV is in use). In particular, you will be using CLUSTER_CONFIG or CLUSTER_CONFIG_LAN to configure the Cluster nodes. The latter is identical to the former, save it uses LANCP for satellite operations. (LANCP is available in OpenVMS V6.2 and later, and eliminates the need for the installation of DECnet Phase IV or DECnet-Plus for access to the MOP protocol used for the initial satellite bootstrap. Once the initial MOP download request is performed, and the image(s) are downloaded via MOP, MOP is not used again.) For various PCI-based systems, there have been PCI CI adapters made available. The Wizard would recommend checking for support on the particular system before proceeding down this path, and would recommend considering the differences in the adapter cost and the available bandwidth. (CI has a higher hardware cost and generally lower system overhead than other adapters, and two paths each with 70 megabit per second throughput.) Other PCI options available include Memory Channel and FDDI, etc. (Classic Ethernet at 10 megabits per second throughput is usually considered quite slow by current performance standards.)
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