MVS/ESA Dataspaces And Hiperspaces - IBM Mainframe

MVS/ESA has extended virtual storage by incorporating data spaces into the processing environment. Data spaces have taken some of the burden of keeping data in virtual storage off of address space. Data spaces also allow greater accessing speeds by reducing I/O. This serves to free uplarge areas of the address space for other uses. Having additional address space for programs allows us to incorporate more functions in them without imparing performance.

There are two types of data spaces. Both may be 2GB in size and this entire amount may be used for data or programs stored as data. The first type is a regular data space. It is backed by main, expanded and auxiliary storage. Data that resides in a regular data space may be address space. The second type of data space is a hiperspace (high performance space). It is backed by expanded and auxiliary storage. Data from a hiperspace must be accessed in 4 K increments and moved to an address space or regular data space for access by program instructions.

Application programs can access data from data space and not from Hiper space. Data spaces contain user data and user Application program. Address space contains OS data and AP data. This isolation ensures no chance of data corruption. Programs can be stored as data in Data spaces but cannot be executed there. MVS/ESA supports High Level Languages such as COBOL,C/370, FORTRAN, PASCAL and PL/I and machine language 370 Assembler. Regular data space is maintained by main, expanded and auxiliary storage. Since it is backed up by main storage, it uses more costly resources than Hiperspaces. Hiperspace is backed up by Expanded and auxiliary storage.

Regular data spaces are byte addressable whereas Hiperspace is 4K addressable. Data cannot be accessed from Hiperspace. The data should be moved to Regular data space or address spaces so that Application programs can access them. While working with High level languages such as COBOL, FORTRAN, PASCAL,PL/I , it is possible to access a Hiperspace. With Assembler (370 Assembler) both Data space as well as Hiperspace can be accessed.

There are two types of data spaces viz., private regular data space and shared regular dataspace. Private regular data space is used by single application. Shared regular data space is used by more than one application program. Regular data space is the best choice for holding data and program when data needs to be manipulated using ESA/370 instructions

Hiper spaces could be used in some applications where there are millions of transactions. Data could be moved in blocks with any I/O, here the data access is just a piece of the application. There are two types of shared regular data space, privileged and non-privileged. Data can be moved from address space to private regular data space or shared regular data space.

There are two types of Hiperspaces viz., Standard Hiperspaces and ESO (Expanded Storage Only). Standard Hiperspace is backed up by Expanded and Auxiliary storage. It provides faster data access than DASD. Only Expanded storage backs up the ESO Hiperspace. ESO also offers still faster data access. But these are reserved for privileged users. Data is stored in buffers of the 4K size increments in both Hiperspaces. Just like data spaces, Hiperspaces help in case of virtual storage constraints. If virtual data are crawling programs in address space, the data could be moved into hiperspaces. Using data spaces will be good idea with reference to file used very frequently. Thus the MVS/ESA offers data spaces and hiperspaces which reduce excessive I/O.

Benefits of using data spaces (regular and Hiperspace):

  • I/O avoidance
  • Isolation of data from programs
  • For data integrity
  • To allow growth of programs without virtual storage constraint
  • Increased virtual storage

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