vtAlpha builds a virtual Alpha computer environment inside a X86 host system to run you software. It translates in real-time between the Alpha and X86 architectures, allowing the original Alpha software to run on X86 without changes.
vtAlpha requires sufficient resources from the host in order to make virtualization effective and efficient. This web page provides guidelines to select the best host environment for your virtual Alpha(s).
Host CPU requirements
Every virtual Alpha CPU requires a full host CPU-core to run. In order to facilitate the Alpha CPU process vtAlpha needs 50% extra CPU capacity on the host for adjacent and supporting tasks. This means every virtual Alpha CPU requires 1.5 Host CPU-core, at a minimum.
For most vtAlpha implementations this will be sufficient. However, for Alphas that were exercised harder it might be necessary to assign extra host CPU-power to keep up with the high performance demand of the Alpha-based software. This can only be assessed by running the user applications. vtAlpha allows to manually assign more host CPU-resources to a certain virtual Alpha by using the "JIT Processors" parameter in the vtAlpha configuration (Advanced Options).
The default value of this parameter is 0, meaning vtAlpha will claim one additional host CPU-core for every vtAlpha instance in the product range vtAlpha-AS - vtAlpha-ES. In case of vtAlpha-GS it claims one additional host CPU-core per QBB. When manually assigned a value other than 0 vtAlpha will allocate that number of host CPUs instead. This allows to assign more than the default setting (note: in the case of vtAlpha-GS you are able to assign less than what is allocated by default).
vtAlpha-AS to vtAlpha-ES:
Alpha CPUs + 50% + additional JIT processes
Alpha CPUs + 50% + QBBs
unless the JIT Processor parameter is used, then the following formula applies
Alpha CPUs + 50% + JIT processors
Minimum CPU specification
The Alpha processor was already a very powerful compute engine, so Alpha virtualization requires quite some X86 CPU-power to match the performance of the original system. We therefore recommend the latest generations of Intel Xeon (v3 or v4) processors with a CPU-frequency of 3 GHz or better. Hyper-threading must be disabled on the host.
Minimum host memory requirement
Also for memory vtAlpha requires a bit more than the original Alpha hardware.
Host memory calculation: Alpha memory + 25% + 1 GB for the host (= vtServer)
Required disk space
Same amount as with the original Alpha system, plus the vtAlpha system partition, which is used the vtAlpha software, virtual Alpha configurations, host configuration settings and log files.
Disk space: Alpha GB + 40 GB (= vtServer partition)
Virtual Machine Host
vtAlpha runs best when installed directly on the X86 hardware (Bare Metal), but it also runs on a Virtual Machine host (VMware, Hyper-V, KVM, Xen). When running on a VM the same host requirements apply as for Bare Metal installation.
Note that by default these Virtual Machine products apply smart allocation mechanisms, allowing their guests to share the host hardware. This may make sense for general purpose environments, but not for Alpha virtualization. vtAlpha must have unshared access to the hardware of the host it is running on, otherwise it may result in performance degradation or even more severe problems. The Alpha Operating Systems OpenVMS and Tru64 expect the Alpha hardware they run on to be available to them in full. Any delay in availability may be assessed as a hardware malfunction by VMS/Tru64, causing it to crash.
It is therefore mandatory to configure the Virtual Machine host such that the virtual Alpha environment receives the resources it requires, without sharing it with other guests on the host VM.