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The Question is: VMS 7.2 changes the restrictions on minimum cluster size on Files-11 volumes to allow more efficent use of new larger disks. It would appear from reading Kirby McCoy's book on Files 11 that ODS2 has been capable of supporting this all along. My question i s: Can earlier versions of OpenVMS properly process a Files-11 volume created on OpenVMS 7.2? If not, what changes have been made to ODS2, and how do you protect earlier versions from accessing these volumes. The Answer is : OpenVMS has not been able to deal with smaller cluster factors, the particular change around support for creating and accessing the larger storage bitmap is new in the OpenVMS V7.2 release. Disks with these newer smaller cluster factors are emphatically not compatible with earlier OpenVMS releases, can not and should not be mounted on releases prior to OpenVMS V7.2. (The OpenVMS documentation should be very clear on this requirement.) Default operations, disk initialization and such will continue to create volumes with cluster factors compatible with earlier OpenVMS versions. Only if the cluster factor settings are explicitly overridden will the new (smaller) cluster factors be available. There is/was no software mechanism available to lock out access to these newer big-bitmap volumes on earlier OpenVMS releases, short of changing the volume structure code and rendering the volume entirely inaccessable by earlier versions. This change would have required changes elsewhere in the V7.2 file system and utilities to correctly enable, configure, detect and process this new volume format code, and was thus this option was not considered feasible for inclusion in the release. Thus the current clearly documented dependence on the "if it hurts, don't do that" solution, and the use of appropriate and compatible default values for the cluster factor.
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