Extended Address Volumes (EAVs)

Before z/OS V1R10, DASD storage was limited to 65,520 cylinders per volume. z/OS V1R10 supports Extended Address Volumes (EAVs), which are by definition 65,521 cylinders or larger. The maximum size of a volume is 262,668 cylinders with z/OS V1R10.

Important

In z/OS 1.13 and higher, an EAV volume can be up to 1 TB in size (1,182,006 cylinders).

The cylinder addresses greater than 65,535 on an Extended Address Volume (EAV) are referred to as the Extended Address Space (EAS). These cylinder addresses are represented by 28-bit cylinder numbers. The cylinders addresses below 65,536 on an extended address volume are referred to as the base addressing space. These cylinder addresses are represented by 16-bit cylinder numbers or by 28-bit cylinder numbers whose high order 12 bits are zero.

The track address with 28-bit cylinder numbers has the following format: track address is a 32-bit number that identifies each track within a volume. It is CCCCcccH in the hexadecimal nibbles format where:

CCCC

is the low order 16 bits of the cylinder number,

ccc

is the high order 12 bits of the cylinder number, and

H

is the four-bit track number.

Extended address volumes are divided into track-managed space and cylinder-managed space.

Track-managed space

is the space on the volume that is managed in tracks and cylinders. Track managed space ends at cylinder address 65,519. Each data set occupies an integral multiple of tracks. Track-managed space also exists on all non-EAV volumes.

Cylinder-managed space

is the space on the volume that is managed only in Multi-Cylinder Units. A Multi-Cylinder Unit (MCU) is 21 cylinders. Cylinder-managed space begins at cylinder address 65,520. Each data set occupies an integral multiple of multi-cylinder units (MCUs). Space requests targeted for the cylinder-managed space are rounded up to the next multi-cylinder unit. Cylinder-managed space only exists on Extended Address Volumes (EAVs). An EAS-eligible data set is one that can be allocated anywhere on an EAV.

EAS-eligible data sets allocated on an EAV are created with Format 8 and Format 9 DSCBs in the VTOC. A Format 8 DSCB is equivalent to a Format 1 DSCB and the Format 9 DSCB provides additional attribute data and a set of pointers to possible Format 3 DSCBs.

For an Extended Address Volume (EAV), the system and storage group breakpoint value (BPV) helps direct DASD space requests to cylinder or track-managed space. The breakpoint value is expressed in cylinders. When the size of a DASD space request is the breakpoint value or greater, the system prefers to use cylinder-managed space for that extent. This rule applies to each request for primary or secondary space for data sets that are eligible for cylinder-managed space. If cylinder-managed space is insufficient, the system uses the track-managed space or uses both types of spaces. When the size of a DASD space request is less than the breakpoint value, the system prefers to use the track-managed space. If space is insufficient, the system uses the cylinder-managed space or uses both types of spaces. The breakpoint value (BPV) is specified in the IGDSMSxx PARMLIB member. This parameter is optional and if not specified, the default value of 10 cylinders is used. A breakpoint value can also be specified for each storage group and overrides any value in the IGDSMSxx PARMLIB member.

EAS-eligible data sets are those that can be allocated anywhere on an EAV. z/OS V1R12 supports the following types of data sets as EAS-eligible data sets:

  • SMS-managed and non SMS-managed VSAM data sets including:
    • BCS and VVDS catalog data sets
    • VSAM data sets inherited from prior physical migrations or copies
    • VSAM temporary data sets
    • zFS data sets (they are VSAM)
  • Sequential data sets, including extended, basic, and large formats
  • PDS and PDSE data sets
  • Direct (BDAM) data sets
  • Data set allocated with undefined DSORGs

Non-EAS eligible data sets are those that can be allocated only in the track-managed space of an EAV volume. For z/OS V1R12, non-EAS-eligible data sets include:

  • HFS data sets
  • PAGE data sets
  • VTOC and VTOC index data sets
  • VSAM data sets with IMBED or KEYRANGE attributes that may have been inherited from prior physical migrations or copies

EATTR=OPT considerations

The FDRDSF RESTORE function and the FDRCOPY COPY and MOVE functions support EATTR=OPT allowing these FDR processes to allocate data sets in the cylinder-managed space of Extended Address Volumes (EAVs). The allocation of data sets in the cylinder-managed space by these FDR processes follow these rules:

  • For a non-VSAM data set, if the file has EATTR=OPT specified in the DSCB, or if the EATTR=OPT keyword is specified on the RESTORE, COPY, or MOVE command and the file does not have EATTR=NO specified in the DSCB, the FDR function allows the allocation to go to cylinder-managed space.
    • A single-volume non-VSAM data set is allowed to round up to a multiple of 21 cylinders according to the normal allocation rules. That is, if the size is equal to or larger than the breakpoint value (BPV; default is 10 cylinders), the data set is allowed to be rounded up and allocated in cylinder-managed space.
    • A multi-volume non-VSAM data set is not allowed to round up. If the size is not a multiple of 21 cylinders, the allocation is allowed to be split between cylinder-managed space and track-managed space. If the size is less than 21 cylinders, the data set is allocated in track-managed space.
  • VSAM clusters are eligible to be allocated in cylinder-managed space by default; EATTR=OPT does not need to be specified.
  • For single-volume VSAM clusters that do not have IMBED or KEYRANGEs, the DEFINE follows the normal rules; if the size of the component is equal to or larger than the breakpoint value, the component is rounded up to a multiple of 21 cylinders and allocated in cylinder-managed space. This applies to both data and index components of single-volume VSAM clusters.
  • A multi-volume VSAM cluster is not allowed to round up.
    • If the part of the data component on the current volume is a multiple of 21 cylinders, it is allocated in cylinder-managed space.
    • If the part of the data component on the current volume is not a multiple of 21 cylinders, and it is in more than one extent, the allocation is allowed to be split between cylinder-managed space and track-managed space. For example, a component with 22 cylinders may get 21 cylinders in cylinder-managed space and 1 cylinder in track-managed space.
    • If the part of the data component on the current volume is not a multiple of 21 cylinders, and it is in one extent, it is allocated in track-managed space with the same size.
    • An index component of a multi-volume VSAM cluster is always allocated in track-managed space with the same size.
  • Clusters that have IMBED or KEYRANGEs are always allocated in track-managed space with the same size.

FDRCPK considerations

To display the values of the larger cylinder numbers and extent lengths, MAPFORMAT=EAV is added and used for the “before” and “after” maps when the volume is an EAV volume. With MAPFORMAT=EAV, the “M” (millions) suffix is used for fields in the combined summary reports when values exceed 999,999.

FDREPORT considerations

Additional fields are added to FDREPORT to display information for cylinder-managed and track-managed space in various formats as well as fields to display the Format 8/9 DSCB counts. By default, AUTOEAVDISK is enabled indicating that FDREPORT is to automatically determine if EAVDISK support should be enabled. This causes new field formats to be expanded causing the format of the generated reports to change for the extent descriptors and counts of bytes, tracks, DSCBs, and data set organization fields. See the October 2013 FYI Newsletter for additional information on EAV and FDREPORT.

SAR considerations

SAR does not support EAV volumes.

 

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