EAVs require hardware and software. Due to the limit of 64 K devices per channel subsystem (CSS), large installations still required more storage space. The introduction of logical channel subsystems (LCSSs) helped to increase the capacity by double and quadruple, but EAVs increase this capacity by potentially 4,000-fold, which is based on a maximum theoretical capacity of 225 TB. The maximum EAV with DFSMS V1.13 is 1 TB.
Extended address volumes
EAVs require IBM DS8000® R4 direct access storage device (DASD) subsystems so that EAVs can be defined, as shown in Figure 6-10 on page 106. For EAVs of 1 TB, DS8800 or DS8700 subsystems and z/OS V1.12 or later are required.
Figure 6-10 EAV DASD model on DS8000 R4
An EAV is divided into two parts: track-managed space for the first 64 K cylinders and cylinder-managed space beyond 64 K cylinders. Cylinder-managed space is in an area that is called the
extended addressing space
(EAS). Cylinder-managed space is allocated inmulticylinder units (MCUs), which are 21 cylinders each. Therefore, the smallest data set size that uses cylinder-managed space is 21 cylinders. This size has implications for space usage. It can affect the allocation of data sets, which also applies to DFSMShsm and how it uses EAVs. See Figure 6-11 on page 107.
Important: Only the EAS of the EAV requires any special support. Even data sets that are
not EAS-eligible can still be allocated on an EAV in track-managed space that is within the first 54 GB.
Chapter 6. Data set format support, record-level sharing, and extended address volumes 107 Figure 6-11 The EAS is cylinder-managed space
EAS-eligible data sets
In EAV R1 (z/OS V1.10), only VSAM data sets were eligible for EAS. At EAV R2 (z/OSV.11), extended format sequential data sets were added. Now at EAV R3 (z/OS V1.12+), almost all data set types are eligible and DFSMShsm is enhanced to support almost all data set types. DFSMShsm EAV support includes almost all data set types:
Sequential, including extended, basic, and large formats
Partitioned data set (PDS) and partitioned data set extended (PDSE)
Basic direct access method (BDAM)
Undefine data set organization (DSORG=U)
Catalogs (basic catalog structure (BCS) and VSAM volume data set (VVDS)
VSAM
z/OS file system (zFS), which is VSAM
The DFSMShsm logic uses the EATTR attribute (as used in IDCAMS DEFINE and ALLOCATE, JCL, dynamic allocation, and DATACLAS) when it performs volume selection. The following data set types are not eligible for EAS:
Page data sets
Volume table of contents (VTOC) and VTOC indexes
Hierarchical file system (HFS)
VSAM with IMBED or KEYRANGE parameters that were inherited from earlier physical migrations or copies
These data sets must remain allocated in track-managed space. HSM is not used to manage page data sets, VTOCs, or VTOC indexes, in any case.
EATTR parameter
To allow users to control the migration of non-VSAM data sets to EAS (during the earlier releases of EAV), a new data set level attribute was defined. Each data set used a new attribute, EATTR, to indicate whether the data set can support extended attributes (that is, format-8 and format-9 data set control blocks (DSCBs)). By definition, a data set with extended attributes can reside in EAS on an EAV. This attribute can be specified for non-VSAM data sets and VSAM data sets.
The following values are valid for this attribute:
EATTR = NO No extended attributes. Allocation can select a volume with or without extended addressing with no preference based on this attribute. However, when the data set created, the data set has an F1 DSCB and cannot have extents in the EAS. NO is the
default for non-VSAM
data sets.EATTR = OPT Extended attributes are optional. The data set can use extended attributes and reside in EAS. This value is the
default for VSAM
datasets.
EATTR handling
EXIT28 is used for restore processing to pass DFSMSdss the attributes of pre-allocated data sets (in particular the EATTR) that are deleted by DFSMShsm before its reallocation.
DFSMShsm uses an IDCAMS, which was modified to recognize the EATTR value on an import of a catalog data set and also passes the EATTR value to an export.
Support for DFSMShsm-owned data sets
HSM data sets can now also be allocated as EAS-eligible in V1.12. By using the SETSYS USECYLINDERMANAGEDSPACE command, migration and backup copies of data sets can be EAS-eligible. Dynamic allocation of PDOx/y, LOGx/y, and JRNL as EAS-eligible is supported, too.
DFSMShsm journal data set
Large and extended format sequential, PDSE, and VSAM data sets can occupy an entire EAV with multiple extents. Since EAV R2 (z/OS V1.11), direct-access device space management (DADSM) allows a single extent to span the track-managed and cylinder-managed space. Therefore, a data set can occupy the entire volume with a single extent. Therefore, the DFSMShsm journal can potentially occupy an entire volume.
Command for EAS for migration and backup
With DFSMShsm V1.12 migration data sets (migration level 1 (ML1) and migration level 2 (ML2)) and backup, data sets can be directed to cylinder-managed space on EAVs. All members of an HSMplex need to be at V1.12 before you can use this function. You can use the SETSYS USECMS command to allow EAS eligibility for migration and backup data sets (Example 6-1).
Example 6-1 MVS SETSYS USECMS command
SETSYS USECYLINDERMANAGEDSPACE(Y|N) SETSYS USECMS(Y|N)
The default is to not use cylinder-managed storage. The status of the
Chapter 6. Data set format support, record-level sharing, and extended address volumes 109
DFSMShsm data mover
Support is added to provide the following functions:
Migration and backup, and recall and recovery of a PDS
Backup and recovery of uncataloged and user-labeled sequential data sets
Backup and recovery of catalogs
Migration and recall of user-labeled sequential data sets
Recovery with a specified pre-allocated data set
ABARS support
Enhancements were made to ABARS to support the additional data set types for z/OS DFSMS V1.12. See “EAS-eligible data sets” on page 107. The enhancements are listed:
If the extended attributes for the EAS-eligible Instruction Data Set are lost during recovery of this data set to non-EAV, message ARC0784I is issued.
The algorithm of aggregate recovery of migrated data sets from the INCLUDE list is changed. For storage requirements for an aggregate group, the calculation of the size of the user catalog and user-labeled data set was corrected, and the message ARC6369I is now issued with the correct space requirement value.
A new algorithm is available to assign the JOBNAME and STEPNAME of the source data set (or a pre-allocated data set) from the ALLOCATE list to the target data set in the same way that DFSMSdss is created.
The EATTR value of a source user catalog from the ALLOCATE list is passed to the target.
Modified messages
The following messages were changed or corrected, or the situations in which they are issued were changed.
ARC0153I
ARC0153I now shows the USECMS status:
ARC0153I SCRATCHFREQ=days, SYSOUT(CLASS=class, COPIES=number, SPECIAL FORMS={form | NONE}), SWAP={YES | NO},
PERMISSION={YES | NO}, EXITS={NONE | exits}, UNLOAD={YES | NO}, DATASETSERIALIZATION= {USER | DFHSM}, USECMS={YES | NO}
ARC0784I
This message is now issued when a recall, recover, or ARECOVER to a non-EAV-capable volume causes the loss of format-9 DSCB data:
ARC0784I EXTENDED ATTRIBUTES FOR DATA SET dsname WERE NOT RETAINED DURING THE RECALL | RECOVER | ARECOVER
ARC6369I
This message is displayed for ABARS support when space is recalculated and corrected for EAS allocation for user catalogs and user-labeled data sets. The format though remains the same:
ARC6369I STORAGE REQUIREMENTS FOR AGGREGATE GROUP agname, ARE: L0=number {K|M|G|T}, ML1=number {K|M|G|T}, ML2=number{K|M|G|T}, TOTAL=number {K|M|G|T}
SMS volume selection
For SMS volume selection on recall, recovery, or ARECOVER, DFSMShsm will pass the DATACLASS value to DFSMSdss and volume selection will be performed by SMS. The only exception is for PDS. The DFSMShsm volume selection logic for SMS PDS data sets will be consistent with the non-SMS volume selection logic.
Non-SMS volume selection
DFSMShsm checks the data set level attribute, EATTR, when it selects a non-SMS volume. The EATTR data set level attribute specifies whether a data set can use extended attributes (format-8 and format-9 DSCBs) and optionally reside in EAS on an EAV. The EATTR attribute is optional. If you specify it, valid values are NO and OPT. For more information about the EATTR attribute, see ALLOCATE and DEFINE CLUSTER in z/OS DFSMS Access Method Services for Catalogs, SC26-7394.
If an EATTR value is not specified for a data set, the following default data set EATTR values are used:
The default behavior for VSAM data sets is OPT.
The default behavior for non-VSAM data sets is NO.
Preference for volume selection corresponds to the EATTR values for each data set:
When EATTR = NO, the data set has no preference to any volume. For recalls, recovers, and ARECOVERs, the volume with the most free space is selected, but only the
track-managed free space is used to determine the free space calculations of an eligible EAV. The data set is allocated with a format-1 DSCB, which indicates that it is not eligible to have extents in the EAS.
If an EAV or non-EAV is chosen for allocation, and the value is EATTR=NO and the data set used a format-8 or format-9 DSCB with vendor attributes, the data set is allocated with a format-1 DSCB. The system issues message ARC0784I to indicate that extended attributes were not retained for this recall, recovery, or ARECOVER. In this situation, the format-9 information of the data set will be lost on the recall, recovery, or ARECOVER.
When EATTR = OPT, the data set prefers EAV volumes if the size of the allocation is equal to or greater than the breakpoint value (BPV) that is specified. If the requested size of the data set allocation is smaller than the BPV, EAVs and non-EAVs have equal preference: – If an EAV is chosen for allocation and the data set type is EAS-eligible, the data set is
allocated with format-8 or format-9 DSCBs in either the track-managed space or the EAS.
– If a non-EAV is chosen for the allocation and the data set used format-8 or format-9 DSCBs with vendor attributes, the data set is allocated with a format 1. Then, DFSMShsm issues the ARC0784I message, which signifies that extended attributes were not retained for this recall, recovery, or ARECOVER. The EATTR value always remains in the format-1 DSCB.
EAV considerations for space management
Because an EAV has two areas, track-managed space and cylinder-managed space (EAS), new selection criteria were added with the TRACKMANAGEDTHRESHOLD parameter. It is used with the THRESHOLD parameter. It was necessary because data set size is also considered when data sets are migrated. Also, data sets in the EAS are larger on average than the data sets that are below in track-managed space. Data sets in the EAS will be migrated before the data sets that are in track-managed space, which might mean that the track-managed space is not freed up.
Chapter 6. Data set format support, record-level sharing, and extended address volumes 111
DFSMShsm examines both volume-level thresholds and track-managed thresholds for L0 EAVs. If either threshold is exceeded, migration eligibility is 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 is 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 is 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 is eligible to be processed when the entire volume space is managed. Table 6-2 shows how selections are made.
Table 6-2 Migration eligibility
For SMS volumes, DFSMShsm uses the track-managed threshold and the volume threshold from the storage group. For non-SMS volumes, the track-managed threshold is specified on the ADDVOL command when you add primary volumes to DFSMShsm:
ADDVOL PROD01 PRIMARY UNIT(3390) TRACKMANAGEDTHRESHOLD(80 40) THRESHOLD(85 60)
If no TRACKMANAGEDTHRESHOLD is specified, the volume threshold values are used, by default.
Support and considerations for 1 TB EAVs
The support for DFSMShsm 1 TB resulted in no external updates. Only internal fields required updating to handle the larger quantities that are dealt with. Although no externals require definition or implementation for DFSMShsm, several considerations are new. Testing shows a considerable increase in elapsed time for IBM HyperSwap® for larger volume capacities due to the larger amounts of metadata. Spreading 1 TB EAVs over as many LSSs as possible is best.
Additionally, although dynamic volume expansion automatically starts reformatting the VTOC so the larger extra capacity that is added is recognized by the VTOC, you still need to manually expand the size of the VTOC, VTOC index, and VVDS to handle the larger number of expected data set entries. Instructions for dynamic volume expansion and expanding the VTOC and VTOC index are covered in Chapter 10 of z/OS V1.13 Technical Update, SG24-7961.
Autodump considerations with EAVs
With the introduction of large capacity volumes, such as EAV, users who use dump stacking need to review DUMP CLASS and its dump stack figure.
A storage group of different capacity volumes (3390 Model 3, Model 9, Model 27, Model 54, and EAV) might require the DUMP window to be extended for DFSMShsm to complete the full volumes dump.
Track-managed threshold exceeded
Volume threshold exceeded Data set selection
Yes No Only data sets with one or more of the first three extents that are allocated in track-managed space
No Yes All data sets
Yes Yes All data sets
A dump task with all high-capacity volumes to be dumped (such as Model 27, Model 54, or EAV) requires more time to complete than another dump task, which only dumps all Model 3 volumes by using the same dump stacking figure.
We recommend that you group the same capacity volumes into the same dump class and assign the appropriate dump stacking figure (the higher the volume capacity, the smaller the dump stacking figure) to prevent large differences between the dump tasks’ elapsed times to complete. This configuration helps minimize the need to extend the dump window.
EAV considerations for recovery functions
You can specify the EATTR value when you allocate a data set to define whether the data set can use extended attributes (format-8 and format-9 DSCBs) and optionally reside in EAS. If a data set is directed to a pre-allocated data set on a RECOVER or ARECOVER function, the system uses the EATTR value of the pre-allocated data rather than the EATTR value that is specified for the data set source recovery data.
New considerations exist for ARECOVER and EATTR. The following methods can be used to allow the EATTR information from the ABACKUP site to be restored, with the data set:
Use the DSCONFLICT(RENAMETARGET) parameter on the ARECOVER command, then manually delete the existing data set. Because the ARECOVER resolved the conflict by renaming the existing data set before it restores the ABARS copy, both copies will have their own EATTR. You need to remove only the renamed existing data set.
Use the DSCONFLICT(BYPASS) parameter on the ARECOVER command, then manually delete the existing data set and existing conflict resolution data set, and then rerun the ARECOVER
command. Only the data sets that were bypassed or failed for another reason on the first ARECOVER will be processed. Because no conflict exists, you will get the ABARS copy, complete with its EATTR.
For more information, see the EATTR parameter of the ALLOCATE command in z/OS DFSMS Access Method Services for Catalogs, SC26-7394.
Recommendations for using EAVs
Because ML1, ML2, and backup volume allocations can reside in either the track-managed space or the cylinder-managed space on an EAV beginning in V1R12, it is important to understand that allocations in the cylinder-managed space are in multicylinder units (MCUs) and can potentially result in an over-allocation.
You might want to evaluate the SMS and non-SMS BPV settings. If possible, enable the system to avoid over-allocation for smaller disk space requests. For larger disk spaces, use cylinder-managed space and allocate in MCUs for larger disk space requests.
For example, setting the BPV to a high value will result in smaller disk space requests made by DFSMShsm more likely to reside in the track-managed area. Larger disk space requests will prefer to use space that can end up in an over-allocation. However, this over-allocation will be a much smaller percentage of the total disk space request and the over-allocation might be acceptable. For more information about using EAVs, see z/OS DFSMS Using the New Functions, SC26-7473.