As someone who has delved deeply into this subject for different reasons, and without "inside" knowledge, here's what I have learned or intuited:
1. Logical volumes are entirely self-contained (think of them as files), allocated from the arrays with all required space needed to hold metadata, including the count and key fields associated with every track allocated to the volume. 2. The CK fields appear to be located within the logical track construct. This does not preclude the existence of other constructs to make key and ID searches go faster. I speculate that such constructs do exist. Why? Because that's what I would do. 3. For thinly-provisioned volumes, space is allocated on WRITE-type operations and is released on ERASE-type operations. Space is managed in chunks that are implementation dependent, not on the architecture, though for DS8K, I think it's 1113 cylinders at a time (3390 mod 1 size). 4. While the architecture allows R0 data to be more than 8 bytes, it's not a good idea. There are too many things that "know" R0 is 8 bytes. 5. The space calculation capacity factors and the algorithm to use are returned by the device via Read Device Characteristics (RDC). You have to go to the book to get the algorithm details. 6. Unformatted track capacity is a useless number to sysprogs. 7. The best utilization of the device is when you have just one user record on the track (R1), and that record is 56664 bytes. 8. READ FULL TRACK and WRITE FULL TRACK operations are very specialized operations typically used only by programs that are archiving/restoring data. 9. "Nobody cares about this stuff, Alan. Don't you have something more important you should be doing?" I have a program that gathers capacity data. Here's output for a 100-cylinder minidisk. The only thing that changes based on cylinder count is the total capacity value: Capacity formula: 2 Capacity factors F1-F6: 34 19 9 6 116 6 HA + R0 length: 1428 Track length: 58786 Max R0 length: 57326 Max R1 length: 56664 (architected) Unformatted device capacity: 84.1 MB Formatted device capacity (4K blocks): 70.3 MB Formatted device capacity (56664 block): 81.1 MB Regards, Alan Altmark IBM z/VM Engineer and Consultant ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN
