Technical Notes—MVS
The following Technical Notes apply to services provided by DCRT. This information supercedes all documentation with earlier publication dates.
Default Disk Type Changes to 3390 (RAMAC)
Since the beginning of the conversion from 3380 devices to the new RAMAC devices, the MVS operating system has converted allocation specifications (TRK, CYL) from the default 3380 units to comparable values on the RAMAC devices. Effective October 2, 1995, the assumed (default) allocation units will become units of RAMAC tracks and cylinders. (Note: RAMAC, 3390, and 3390-3 are synonymous.) The most important result of this change in the default unit is that if you are currently allocating in TRKs or CYLs, and you do not change your allocation, as of October 2 you will be allocating about 18 percent more space than is currently the case.
During the conversion, users had no knowledge of where data sets were going to be allocated on public storage because of the mixed device environment. Automatic conversion for allocations to public space removed the requirement for users to know the specifics of the device to which the data were being assigned. The default allocation is being changed to reflect the fact that all public space is now implemented on RAMAC devices.
Automatic conversion has been in effect for public storage only (FILE, TMP, MSS, SYSDA). Allocation to dedicated disks has, and will continue to be, in units of the actual device being allocated. That is, if the device is a 3380, then 3380 units will be used, and if it is a RAMAC, then RAMAC units will be used. As a dedicated device is converted to RAMAC, users should make appropriate changes in their allocation specifications to reflect this change in device types.
To assist allocation to all devices, the ENTER DISKCALC command procedure (CP) has been changed to include the ability to calculate and recommend space allocations on both the 3380 and the RAMAC devices. In addition, as of October 2, 1995, the ENTER DISKCALC CP will change its default units to RAMAC. The CP remains largely unchanged, except for the ability to specify RAMAC or 3390 as the device type and additional comments at the beginning referring to use of system-selected space allocation.
Even though the ENTER DISKCALC CP enables you to compute recommended allocation values, the best solution is to let the system pick both the BLKSIZE and space allocation for you. Letting the system do the determination will eliminate all device dependencies, both current and future. This will allow optimal space allocation and utilization for any device, whether for public devices or for dedicated devices. The mechanism for invoking system selection of BLKSIZE and space allocation involves omitting the BLKSIZE parameter and doing the space allocation in terms of RECORDS, rather than tracks or cylinders. INTERFACE 188, page 26, has the complete description of the methods involved. The revised Users Guide, due out in September 1995, will also have this information.
Interface 192 (September 15, 1995)