Consider the following points before migrating z/OS 2.3 to IBM z15™: HyperSwap support is enhanced to allow RESERVE processing. When a system runs a  request to swap to secondary devices that are managed by HyperSwap, z/OS detects when  RESERVEs are held and ensures that the devices that are swapped also hold the RESERVE.  This enhancement is provided with collaboration from z/OS, GDPS HyperSwap, and CSM  HyperSwap. IBM preview announcement for z/OS Version 2 Release 4 was made available through  Announcement letter 219-013 on Feb. 26, 2019. Focusing on three critical areas (Security,  Simplification, and Cloud), IBM z/OS V2.4 operating system intends to unleash innovation  through an agile, optimized, and resilient platform that helps clients to build applications and  services that are based on a highly scalable and secure infrastructure. This infrastructure  delivers the performance and availability for on-premises or provisioned as-a-service  workloads that enable businesses to digitally transform. IBM z14 supports z/VM 7.1 and z/VM 6.4. z/VM is moving to continuous delivery model. For  more information, see this web page. z/VM 7.1 can be installed directly on IBM z15. z/VM V7R1 includes the following new  features: 7.6.1 z/VM 7.1 7.6 z/VM migration considerations 7.5.6 z/OS V2.4 GLYPH<SM590000> IBM z/OS V2.3 with z15 requires a minimum of 8 GB of memory. When running as a z/VM  guest or on an IBM System zfi Personal Development Tool, a minimum of 2 GB is required  for z/OS V2.3. If the minimum is not met, a warning WTOR is issued at IPL.  GLYPH<SM590000> Dynamic splitting and merging of Coordinated Timing Network (CTN) is available with z15. GLYPH<SM590000> The z/OS V2.3 real storage manager (RSM) is planned to support a new asynchronous  memory clear operation to clear the data from 1M page frames by using I/O processors  (SAPs). The new asynchronous memory clear operation eliminates the CPU cost for this  operation and help improve performance of RSM first reference page fault processing and  system services, such as IARV64 and STORAGE OBTAIN. GLYPH<SM590000> RMF support is provided to collect SMC-D related performance measurements in SMF 73  Channel Path Activity and SMF 74 subtype 9 PCIE Activity records. It also provides these  measurements in the RMF Postprocessor and Monitor III PCIE and Channel Activity  reports. This support is also available on z/OS V2.2 with PTF UA80445 for APAR  OA49113. GLYPH<SM590000> Single System Image and Live Guest Relocation included in the base. In z/VM 6.4, this  feature was the VMSSI-priced feature. GLYPH<SM590000> Enhances the dump process to reduce the time that is required to create and process  dumps. Continuing with less than the minimum memory might affect availability. A migration health  check will be introduced at z/OS V2.1 and z/OS V2.2 to warn if the system is configured  with less than 8 GB. 324  IBM z15 (8561) Technical Guide