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The Question is: I have a VAX 7640 running OpenVMS V6.2 with 1GB of memory. The system is configured with 3 PAGEFILE.SYS of approximately 1 million blocks each. All three are on non-system disks. There is no SWAPFILE configured or installed. My system administrator says that if required, the system will use the available PAGEFILE for process swapping. My question(s) are : 1) Is that true? 2) Is it advisable? 3) What if "Reservable" PAGEFILE is a negative number? 4) Doesn't a "minimum" VMS boot require a PAGEFILE.SYS on the system disk? The Answer is : OpenVMS can and will swap to the PAGEFILE if necessary, and if the PAGEFILE has sufficient space, and if this behaviour has not been disabled via the dynamic system parameter NOPGFLSWP. Swapping to the PAGEFILE is generally not an issue, as most OpenVMS systems -- save for those that are severely memory-constrained -- do not swap. If the processes are swapped out, they first get their working sets trimmed back, thus relatively few pages need be swapped. For reasons of performance, pagefiles should generally be oversize, and they can (should) be scattered across disk spindles, based on the system, paging, and disk spindle I/O loads. A minimally booted OpenVMS system with 1 GB of memory will operate for a considerable interval before the system is likely to stall. (OpenVMS does not support processes that are started up before the PAGEFILE(s) are connected, and that run for long intervals. Cases that are known to have caused problems include bootstrapping with STARTUP_P1 set to MIN (and with no pagefiles connected), followed by logging in and performing many image activations -- it best to mount the disks, connect the pagefiles, and SPAWN to perform the necessary commands.) Swapping is generally only common when it is more efficient to free up system memory by tossing out large processes in their entirety. See the system parameter SWPOUTPGCNT for details on how to control this. When swapping occurs "naturally" on a memory-constrained OpenVMS system, system performance is generally such that swapping to the SWAPFILE or to the PAGEFILE is not a central performance issue -- the system is better served through the acquisition of more physical memory or the reduction of peak physical memory requirements. For details on the negative number in the reservable pages, please see the FAQ section "MGMT17. Why do I have negative number in the pagefile reservable pages?"
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