ⓘ Virtual Storage Access Method
Virtual Storage Access Method is an IBM DASD file storage access method, first used in the OS/VS1, OS/VS2 Release 1 and Release 2 operating systems, later used throughout the Multiple Virtual Storage architecture and now in z/OS. Originally a record-oriented filesystem, VSAM comprises four data set organizations: Key Sequenced Data Set, Relative Record Data Set, Entry Sequenced Data Set and Linear Data Set. The KSDS, RRDS and ESDS organizations contain records, while the LDS organization simply contains a sequence of pages with no intrinsic record structure, for use as a memory-mapped file.
IBM uses the term data set in official documents as a synonym of file, and direct access storage device hard, because it supported other devices similar to disks.
VSAM records can be fixed length or variable length. They are organized in fixed-size blocks called control intervals CIS and then into larger divisions called control areas CASS. The interval size control is measured in bytes, e.g. 4 KB and the size of the control zone are measured in disk tracks or cylinders. Intervals control the units of transfer between disk and computer so a read request will read one complete control interval. Control areas are the units of allocation so, when you define a VSAM data set a whole number of control areas will be highlighted.
Access method services IDCAMS utility is often used to manipulate the delete and define the VSAM datasets.
Custom programs can access VSAM datasets through data definition DD statements in the job Control language JCL by using dynamic allocation or in online regions such as in the information control system CICS.
Both IMS / DB and DB2 are implemented on the basis of VSAM and use its underlying data structures.
- sequential access method BPAM - Basic partitioned access method ISAM - Indexed sequential access method VSAM - Virtual storage access method introduced
- comparable with the Virtual Storage Access Method VSAM which was at that time a new and supposedly converged access method for disk storage Originally, VTAM
- method QISAM Basic partitioned access method BPAM Basic direct access method BDAM Virtual storage access method VSAM IBM in its 1964 first version
- store. ISAM was replaced at IBM with a methodology called VSAM virtual storage access method Still later, IBM developed DB2 which, as of 2004, IBM promotes
- granularity or access granularity. One common method to address these limits is to use multiple levels of virtualization In several storage systems deployed
- Single Virtual Storage SVS refers to Release 1 of Operating System Virtual Storage 2 OS VS2 it is the successor system to the MVT option of Operating
- several notable caveats. Access to physical system resources such as the network access display, keyboard, and disk storage is generally managed at
- optical methods Magneto - optical disc storage is non - volatile, sequential access slow write, fast read storage used for tertiary and off - line storage 3D
- computer hardware platforms, storage devices, and computer network resources. Virtualization began in the 1960s, as a method of logically dividing the system
- A storage area network SAN or storage network is a computer network which provides access to consolidated, block - level data storage SANs are primarily
- Its file formats and procedures are similar to those of the Virtual Storage Access Method VSAM product offered by IBM for its mainframe computers and