Orientación y objetivos del documento

A POOL storage group describes a grouping of DASD on which data sets reside. Figure 4-1 shows the ISMF Pool Storage Group Alter panel for the DB8B storage group in our

environment.

Figure 4-1 Storage group attributes

Several DFSMShsm functions are managed at a storage group level:

 Space management

 Availability management: – Automatic backup processing – Automatic dump processing

You can also control which system performs what functions against the volumes of a storage group at the system or system group level.

The storage group specifications determine only how DFSMShsm automated processing processes the volume. They have no impact on how commands that are directed to the volume or against data sets that are allocated on the volume are processed.

DGTDCSG2 POOL STORAGE GROUP ALTER Page 1 of 2 Command ===> SCDS Name . . . : SYS1.SMS.MHLRES3.SCDS Storage Group Name : DB8B To ALTER Storage Group, Specify: Description ==> DASD FOR DB2 V8 DB8B ==> Auto Migrate . . N (Y, N, I or P) Migrate Sys/Sys Group Name . . Auto Backup . . N (Y or N) Backup Sys/Sys Group Name . . Auto Dump . . . N (Y or N) Dump Sys/Sys Group Name . . . Overflow . . . . N (Y or N) Extend SG Name . . . Copy Pool Backup SG Name . . . SGCPB1 Dump Class . . . (1 to 8 characters) Dump Class . . . Dump Class . . . Dump Class . . . Dump Class . . . ALTER SMS Storage Group Status . . . N (Y or N) ALTER SMA Attributes . . . N (Y or N) Use ENTER to Perform Selection; Use DOWN Command to View next Page;

4.2.1 Space management

Both primary space management and interval migration are determined by the storage group that is assigned to the first extent of the data set. This determination occurs whether or not a data set is eligible for processing by space management. If a data set extends over more than one storage group (for example, a primary storage group and an extend storage group), the settings of the storage group where the first extent of the data set resides are critical. Two separate parameters determine whether DFSMShsm processes data from the volumes in a storage group. Both of these parameters are set at the storage group level (not the volume level).

The first parameter that you define is the migration attribute of a storage group with the “Auto Migrate” attribute. The second attribute consists of a high and a low allocation threshold that determines whether any particular volume is targeted by a particular run of space

management.

Auto Migrate attribute

The following options are available when you determine whether DFSMShsm space management processes data:

N DFSMShsm will not process this volume during space management.

Y This setting is the default setting for a pool storage group. DFSMShsm processes data sets from volumes in this storage group during primary space management. Volumes are targeted by primary space

management until either the volume falls below its “MIGR LOW” threshold or no more data sets that are eligible to be migrated are on the volume.

If SETSYS INTERVALMIGRATION was issued, volumes in a storage group are also eligible for interval migration processing.

I Data sets on volumes in a storage group that are defined as AM=I are eligible for processing by both primary space management and interval migration regardless of the setting of SETSYS

INTERVALMIGRATION.

P Data sets are eligible for primary space management but not interval space management regardless of the setting of SETSYS

INTERVALMIGRATION.

Thresholds

Storage groups are assigned both a low and a high allocation threshold. Thresholds apply at the volume level. Thresholds are specified as a percentage of the space in the storage group. Thresholds are applied as a percentage of the space for each volume so where storage groups consist of volumes of different capacities, thresholds are applied according to each volume’s capacity.

A volume that is over its high allocation threshold can still be targeted for new allocations if no other volume is available in the eligible storage groups with sufficient space to accommodate the data set.

Low allocation threshold

Chapter 4. SMS and its interactions with DFSMShsm 63

During primary space management, data sets are processed until either the allocated space on the volume drops below the storage group low allocation threshold or until DFSMShsm can find no more data sets on the volume that are eligible for processing.

High allocation threshold

The default high allocation threshold is 85. During interval migration, DFSMShsm moves eligible data sets from each volume with allocation at or above the MIGR HIGH value until the allocation reaches the MIGR LOW value. When Auto Migrate is I, migration is performed when the space that is used exceeds the halfway mark between the HIGH and LOW thresholds.

Migrate system/system group name

The default value is blank. By specifying a system or system group, you can restrict

DFSMShsm space management to only process volumes in this storage group on the system or system group that is specified.

4.2.2 Availability management

When you define a pool storage group, you define settings for both automatic backup and automatic dump processing.

Automatic backup processing

Enabling automatic backup processing for a storage group is a binary choice. By default, the following Auto Backup attributes are enabled for pool storage groups:

N DFSMShsm availability management does not target data sets whose primary extent is on volumes in this storage group during automatic backup processing.

Y DFSMShsm availability management targets data sets whose primary extent is on volumes in this storage group during automatic backup processing.

You can also limit processing to a single system or system group by specifying a system or system group name, which is similar to the configuration for space management.

Automatic dump processing

Although the automatic dump process is part of DFSMShsm availability management, you can specify the Auto Dump attribute of a storage group independently of the Auto Backup attribute.

Auto Dump attribute

Two settings are possible for the Auto Dump attribute: Y to enable automatic dump processing and N to disable it. The default setting for the Auto Dump attribute for a pool storage group is

N.

If you use overflow and extend storage groups for automatic dump processing, these groups must be managed in the same way as the primary storage group. This approach ensures that all data that was targeted to this storage group is managed in the same way.

Dump classes

Each pool storage group can be assigned 1 - 5 DFSMShsm dump classes. As with automatic migration and automatic backup, you can also limit automatic dump processing of a storage group to a specific system or system group.