An extended address volume (EAV) is defined to be any volume that has more than 65,520 cylinders. Volumes that are configured with 65,520 cylinders or less are defined to be non-EAVs. An EAV will consist of two areas of managed space. The first 65,520 cylinders of an EAV will be considered the track-managed space. The last cylinder in this managed space is at cylinder address 65,519. The space above 65,520 cylinders will be considered the cylinder-managed space on the volume. The first cylinder in this managed space is at cylinder address 65,520.
Data set size is a determining factor for the order in which data sets are migrated. Managing an entire extended address volume (EAV) with one threshold is not sufficient because average data set size in the cylinder-managed space will likely exceed the average data set size in track-managed space. This will result in data sets allocated in the cylinder-managed space being migrated at a higher rate than data sets allocated in the track-managed space, potentially causing no space in the track-managed space being freed. To prevent this, a unique threshold for the track-managed space (track-managed threshold) is used to manage the free space separate from the free space on the entire volume (volume-level threshold).
DFSMShsm examines both volume level thresholds and track-managed thresholds for L0 EAVs. If either threshold has been exceeded then migration eligibility will be performed for data on the volume. If track-managed threshold values are not specified, the default is to use the volume-level threshold values. Data set eligibility will be further qualified by the location of the first three extents of the data set. If any of the first three extents are allocated in track-managed space the data set will be eligible to be processed when the track-managed space or entire volume space is managed. If none of the first three extents are allocated in track-managed space, the data set will be eligible to be processed when the entire volume space is being managed. Table 1 summarizes the eligibility criteria for migration.
| Track-managed threshold exceeded | Volume threshold exceeded | Data set selection |
|---|---|---|
| Yes | No | Only data sets with one or more of the first three extents allocated in track-managed space |
| No | Yes | All data sets |
| Yes | Yes | All data sets |
| No | No | Data sets are not selected |
Space management (interval migration and primary space management) will be considered complete after DFSMShsm determines both thresholds have been met. This applies only to hourly (interval migration) space management of non-SMS L0 EAVs and when the AUTOMIGRATE attribute is not equal to I (immediate) for SMS-managed EAVs. Hourly space management (interval migration) of SMS-managed EAVs having the AUTOMIGRATE=I attribute in storage groups will be performed if either the midpoint between the high and low volume threshold values is met or if the midpoint between the high and low track-managed threshold values is reached or exceeded. Daily space management (primary space management) will be performed regardless of the high volume threshold and high track-managed threshold values.