Global Resource Serialization
Encyclopedia
Global Resource Serialization (GRS) is the component within the IBM
z/OS
operating system responsible for enabling fair access to serially reusable computing resources, such as datasets and tape drives or virtual resources, such as lists, queues, and control blocks. Programs can request exclusive access to a resource (which means that program and all subsequent requesting programs are blocked until that program is given access to the resource), usually requested when a program needs to update the resource or shared access (which means that multiple programs can be given access to the resource), usually requested when a program only needs to query the state of the resource. GRS manages all requests in FIFO (first in/first out) order.
IBM
International Business Machines Corporation or IBM is an American multinational technology and consulting corporation headquartered in Armonk, New York, United States. IBM manufactures and sells computer hardware and software, and it offers infrastructure, hosting and consulting services in areas...
z/OS
Z/OS
z/OS is a 64-bit operating system for mainframe computers, produced by IBM. It derives from and is the successor to OS/390, which in turn followed a string of MVS versions.Starting with earliest:*OS/VS2 Release 2 through Release 3.8...
operating system responsible for enabling fair access to serially reusable computing resources, such as datasets and tape drives or virtual resources, such as lists, queues, and control blocks. Programs can request exclusive access to a resource (which means that program and all subsequent requesting programs are blocked until that program is given access to the resource), usually requested when a program needs to update the resource or shared access (which means that multiple programs can be given access to the resource), usually requested when a program only needs to query the state of the resource. GRS manages all requests in FIFO (first in/first out) order.
Scoping
GRS manages resources at three different levels of scoping:- STEP - this level is for resources that exist within a single MVSMVSMultiple Virtual Storage, more commonly called MVS, was the most commonly used operating system on the System/370 and System/390 IBM mainframe computers...
address space. Only threads (tasks) within that address space can request access to the resource. - SYSTEM - this level is for resources that exist within a single MVS instance. Any thread running on the system can request access to the resource.
- SYSTEMS - also known as GLOBAL, these resources are accessible by multiple MVS instances. Any thread running on a system in the GRS complex can request access to the resource.
Clustering
In order for GRS to serialize resources between multiple systems, the systems must be clustered. There are several options to enable this clustering:- GRS Ring - each of the systems (LPARLPARA logical partition, commonly called an LPAR, is a subset of computer's hardware resources, virtualized as a separate computer. In effect, a physical machine can be partitioned into multiple logical partitions, each hosting a separate operating system....
s) are connected with channel-to-channel adapters (CTCAs) in a ring configuration. The GRS software sends messages around the ring to ensure the integrity of the complex and to arbitrate correct succession of ownership. - Basic Sysplex - each of the systems in the sysplex has complete connectivity to every other system via CTCAs or ESCON CTCAs, managed by the XCF (Cross System Coupling Facility) component. The GRS component utilizes the Messaging and Group Services provided by XCF to replace and augment the function through the GRS managed CTCAs.
- GRS Star (Parallel SysplexIBM Parallel SysplexIn computing, a Parallel Sysplex is a cluster of IBM mainframes acting together as a single system image with z/OS. Used for disaster recovery, Parallel Sysplex combines data sharing and parallel computing to allow a cluster of up to 32 systems to share a workload for high performance and high...
) - Rather than using a message passing protocol to manage resource ownership succession, GRS uses the locking services provided by the XES (Cross System Extended Services) component of MVS. Use of locking services requires a lock structure (called ISGLOCK) to be created in a Coupling Facility (CF).