EAV
Extended address volume: a very large disk volume, beyond the old limit of 65,520 cylinders, used to hold more data on fewer volumes.
Also written extended address volume, 3390-A, cylinder-managed space, EAS
Traditional 3390 volumes could have at most 65,520 cylinders, about 55 GB. As data grew, sites needed thousands of volumes, which is hard to manage. An extended address volume, or EAV, removes that limit. EAVs, defined as device type 3390-A, can hold up to about a terabyte each.
The space on an EAV is divided in two. The first 65,520 cylinders work as on any volume. The space beyond them is called cylinder-managed space, and in it, space is given out in units of 21 cylinders at a time.
Most modern dataset types can use cylinder-managed space, so most programs work on EAVs without any change. Some older types, or older programs that read disk addresses themselves, may need care, which is why EAV adoption was done step by step at many sites.
For most users, an EAV is just a volume. You will meet the term in storage discussions, in SMS settings that decide which datasets may go on EAVs, and when small space requests turn into 21-cylinder allocations.
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- VolumeA single unit of disk storage with a six-character label, on which datasets are placed.
- Tracks and cylindersThe units used to request disk space on z/OS, taken from the layout of the 3390 disk.
- DASDDirect access storage device, the mainframe term for disk storage.
- ExtentOne continuous piece of disk space belonging to a dataset; a dataset grows by adding extents.
- SMSThe 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.