SMS
The Storage Management Subsystem: the z/OS feature that decides where new datasets go and how they are backed up, kept and deleted, using rules the site writes.
Also written DFSMS, Storage Management Subsystem, storage class, management class, data class, storage group, ACS routine
SMS, the Storage Management Subsystem, is part of DFSMS, z/OS's set of storage functions. It takes decisions about storage away from individual users and applies the site's rules instead.
When a dataset is created, routines written by the site, called ACS routines, look at things like its name and who is creating it, and give it up to four classes. The data class can supply attributes, such as record format and space, so you do not have to code them. The storage class says what performance it needs. The management class says how often to back it up, when to move it to cheaper storage and when to delete it. The storage group is the pool of volumes it will be placed on.
This is why you usually do not name a volume when you create a dataset. SMS picks one from the right pool. Datasets managed by SMS must be catalogued, which keeps them findable by name.
If a dataset ends up somewhere unexpected, or is deleted or moved sooner than you hoped, the explanation is usually in its SMS classes. Storage administrators own these rules.
Where can I learn this hands-on?
Right here, at ZedBank. You take a junior job at a simulated bank and learn each part of the work by doing it, with Zed beside you. There's nothing to install.
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- DASDDirect access storage device, the mainframe term for disk storage.
- VolumeA single unit of disk storage with a six-character label, on which datasets are placed.
- Space allocationReserving disk space for a dataset up front, in tracks, cylinders or blocks, with room to grow.
- High-level qualifierThe first part of a dataset name, which usually identifies the owner and drives how security and storage rules apply.
- CatalogThe system's index of where datasets live, so you can refer to a dataset by name without knowing which disk it is on.
- DFSMShsmThe z/OS storage manager that moves datasets you have not used for a while to cheaper storage, and brings them back when you need them.