IBM OS/390 User Manual
26.6 Shared DASD vs. Cloned DASD
The issue of whether to share DASD volumes and data sets between systems is
decided on the basis of DASD space availability, need for multiple versions of a
file, and the ability to manage updates between the two systems.
decided on the basis of DASD space availability, need for multiple versions of a
file, and the ability to manage updates between the two systems.
26.6.1 Shared DASD between OS/390 Test Systems (vs. Cloned DASD)
The decision to share data sets and volumes or to make copies of them for each
OS/390 system should be thought out carefully. Many OS/390 data sets and some
volumes can be shared between multiple systems as long as updates are
serialized and good change control procedures are followed. The recommended
approach is to put multiple OS/390 systems in the same sysplex and use GRS to
guarantee serialization of these resources. The alternative is to
OS/390 system should be thought out carefully. Many OS/390 data sets and some
volumes can be shared between multiple systems as long as updates are
serialized and good change control procedures are followed. The recommended
approach is to put multiple OS/390 systems in the same sysplex and use GRS to
guarantee serialization of these resources. The alternative is to
″
clone
″
or make
copies of the volumes or data sets, but this obviously takes more DASD space.
Referring to Table 45 on page 403, there are some volumes that can be shared
between active OS/390 systems, and others that should never be shared:
between active OS/390 systems, and others that should never be shared:
System Libraries
Separate SYSRES volumes should be maintained for each
logical OS/390 system.
logical OS/390 system.
Distribution Libraries
Share, but only update from the maintenance system.
Catalogs
The master catalog should be fairly static, contain only
the necessary entries, with the rest in user catalogs. The
master catalog can be shared but highly controlled as to
who can update it. User catalogs can be shared between
systems, use GRS or manual procedures to serialize
updates.
the necessary entries, with the rest in user catalogs. The
master catalog can be shared but highly controlled as to
who can update it. User catalogs can be shared between
systems, use GRS or manual procedures to serialize
updates.
Paging Data Sets
Use by only one system at a time (re-use by different test
system as long as they are not both active at once.)
system as long as they are not both active at once.)
Spool & Checkpoint
JES2 can share the spool and checkpoint between
multiple members if you are comfortable with
multi-access spool. Otherwise, they should be dedicated
to each OS/390 system. The backup OS/390 system
should have its own spool and checkpoint.
multiple members if you are comfortable with
multi-access spool. Otherwise, they should be dedicated
to each OS/390 system. The backup OS/390 system
should have its own spool and checkpoint.
Softcopy Library
Share these between all OS/390 systems.
DFSMShsm ML1
Share if using HSM on both systems.
Storage/Work
Share or isolate depending on how much space you want
to reserve for the
to reserve for the
″
production
″
system.
User Libraries
You can share the user program and data libraries, but
you must keep track of separate version levels with
different data set names or different user catalogs and
volumes.
you must keep track of separate version levels with
different data set names or different user catalogs and
volumes.
A lot of these decisions whether to share volumes, data sets and work space
depends on how much you want to isolate the systems and manage change
control.
depends on how much you want to isolate the systems and manage change
control.
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