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OS/390 systems managed storage (DFSMS) provide enhanced system resource
allocation and management. The Hierarchical Storage Manager (HSM),
Removable Media Manager (RMM) and basic storage device allocation of
OS/390 provide functions not inherent in the VSE environment. However, some
of these functions are available from independent software vendor (ISV)
products.
1.3.3 Connectivity
Connectivity, that is the ability to connect to other systems, has been one of
those areas where VSE support has lagged behind OS/390 and VM. For example
ACF/VTAM support for channel-to-channel connections between host systems
was not introduced until VSE/AF 2.1.3. Lack of other connectivity support, that is
VTAM APPN, SNI gateway, full function TCP/IP and OSA-2, has only added to the
reasons why VSE users have decided to migrate to OS/390. However, as
mentioned, VSE/ESA has since provided support for some of these capabilities,
namely OSA-2 and VTAM APPN. VSE now enjoys virtually all of the same
communications and connectivity capabilities as OS/390 and VM.
1.3.4 Systems Availability
Systems availability has always been a strong requirement for many information
systems environments. Hardware and software technology enhancements in both
VSE and OS/390 have brought about increased system availability. OS/390,
however, has had at its core key design elements that give it premier system
availability characteristics. Advanced S/390 hardware features coupled with
OS/390 software functions give it this outstanding capability. VSE users have
found the attractiveness of this enhanced systems availability capability, along
with other features, yet another reason to embark on an OS/390 migration.
An example of OS/390 enhanced systems availability is the 3990 Concurrent
Copy function when used along with BWO (Backup-While-Open) by DFSMSdss
which allows backups to be taken with integrity even when control area and
control interval splits and data set additions (new extents or add-to-end) are
occurring for VSAM key sequenced data sets. Backup-while-open for CICS
VSAM files supports SMS managed data sets without the need to close a CICS
VSAM data set or to bring applications down to back up VSAM data sets. This
support for backing up VSAM files while open for update is provided in
conjunction with MVS Data Facility Product (MVS/DFP).
In the Parallel Sysplex environment concurrent coupling link maintenance allows
the replacement of a failing coupling link without powering the CEC down. With
DB2 for OS/390 copies of DB2 tablespaces can be made using DFSMS
concurrent copy, a process that significantly improves data availability by
reducing the time necessary to complete logically consistent copies of
mission-critical data.
Chapter 1. Why Customers Migrate 11