Fast Minidisk Erase
Abstract
New function Fast Minidisk Erase improves the speed with which DirMaint erases a minidisk. It also improves the speed at which ICKDSF formats a real volume. The speed improvement is achieved through exploitation of the Locate Record and Erase (LRE) CCW. In our measurements, the time needed for the new function to erase a 32767-cylinder minidisk was 36 seconds, compared to 399 seconds for CMS FORMAT and 253 seconds for CPFMTXA.
PTF UM35563 for APAR VM66288 (CP), plus PTF UV99356 for APAR VM65784 (DirMaint), plus PTF UI64239 for APAR PH14249 (ICKDSF) implements the new function.
Customer results will vary according to system configuration and workload.
Background
Erasing a whole minidisk has traditionally been done with one of two techniques. One way to do this is with the CMS FORMAT command. CMS FORMAT does one I/O per track of the minidisk. Another way to do this is with CPFMTXA. CPFMTXA does one I/O per cylinder. Each of those two techniques runs with corresponding performance; CPFMTXA is a little better performer than CMS FORMAT.
DirMaint erases minidisks before returning their extents to the free extent pool. The speed with which DirMaint can erase a minidisk has become more important as minidisks have become larger. With EAV volumes the minidisks are now so large that DirMaint needed a better technique.
IBM developed a CMS utility program that uses a different kind of channel program to erase minidisks. The new utility program, HCPFER, uses the Locate Record and Erase (LRE) CCW and issues channel programs containing up to 40 LREs. Thus erases can be done much more quickly than in the past.
This article compares results achieved when erasing a large minidisk with CMS FORMAT, and with CPFMTXA, and with HCPFER.
Method
A 32767-cylinder minidisk was obtained. z/VM 7.1 versions of CMS FORMAT and CPFMTXA were also obtained. Finally, a pre-GA copy of HCPFER was obtained. The minidisk was erased with each method. Elapsed times and I/O counts were collected.
Results and Discussion
Table 1 gives the results of our experiments.
| Table 1. Erasing a Minidisk. | |||
| Technique | FORMAT | CPFMTXA | HCPFER |
| Cylinders erased | 32767 | 32767 | 32767 |
| Elapsed time (seconds) | 399 | 253 | 36 |
| Number of I/Os performed | 491552 | 32831 | 50 |
| I/Os per cylinder | 15 | 1 | 0.0015 |
| Notes: CEC model 3906-M05. Dedicated partition. z/VM 7.1 internal driver. Pre-GA edition of HCPFER. | |||
Summary
Compared to the classic methods CMS FORMAT and CPFMTXA, Fast Minidisk Erase improves performance of erasing a minidisk.