•Evaluación y presupuesto de la mercadotecnia •Plan de mercadotecnia
III. Misión de la empresa
A major function of DFSMShsm is space management. With space management, you can keep DASD space available for users on a daily and hourly basis to meet the service-level objectives for your system. The purpose of space management is to manage your DASD storage efficiently so you do not have to.
Space management encompasses the following activities:
Freeing over-allocated space through partial release
Deleting expired data sets
Note: When the backup version is deleted, the space where it was is no longer available
and cannot be used to recover the data set.
Flag Backup Version Deleted
BCDS
DFSMShsm
Chapter 1. DFSMShsm overview 11 Migration of data by moving eligible data sets that were not used recently to an ML1 or
ML2 volume:
– Data movement from expensive volumes to less expensive storage is called
migration
. Data can be migrated from user volumes that users can access to ML1 volumes. The ML1 volumes must be DASD volumes. Data can also be migrated to ML2 volumes, which are usually tape volumes. Although ML2 volumes can be DASD, SMS supports only ML2 tape.– Recall: When the data set is needed again, DFSMShsm returns it to the user’s control. This process is called
recall
and is usually processed automatically by DFSMShsm. Recall is also possible by issuing an HRECALL command from your Time Sharing Option (TSO) session or batch job. The SMS ACS routines ultimately determine the volume to which the data set is recalled.Extent reduction
Space management is achieved through the following phases:
Primary space management
Secondary space management
Interval migration
On-demand migration
This process ensures that only active data occupies space on DASD volumes. Space management parameters control how DFSMShsm makes space available on level 0 volumes. Space management is specified as a combination of parameters in the management classes and storage groups. When planning for space management, you want to strike a balance between enough available DASD space for new data set allocations and frequent recalls of migrated data sets. The management class attributes apply on a data set basis so that different data sets on the same volume can be migrated based on different criteria.
1.6.1 Recycle activity
The data that DFSMShsm stored on tapes is invalidated over time by the expiration of migrated data sets or the generation of more recent backup data sets. The
recycle
function provides the capability of moving the valid data sets out from the original tapes andconsolidates the data on another tape. One tape contains all unexpired data sets and leaves the recycled tapes available for scratching.
1.6.2 Primary space management
During primary space management, DFSMShsm combines a set of specific functions to accomplish DASD usage levels that are coded in storage group (SG) definitions. For non-SMS-managed volumes, they are defined in the DFSMShsm PARMLIB member ARCCMDxx.
The following functions are performed by DFSMShsm during primary space management:
Release unused over-allocated space of eligible data sets
Delete expired and temporary data sets
Migrate data sets to ML1 or directly to an ML2 volume
Whether or not to delete or migrate rolled-off generations if the data set was a member of a generation data group (GDG)
Note: All data sets that are stored in the same non-SMS volume have the same backup
The first functions that are started by primary space management include checking level 0 volumes for temporary and expired data sets that are eligible for deletion. DFSMShsm also releases unused and over-allocated space from eligible data sets and migrate-eligible data sets that were recalled recently, by using the Fast Subsequent Migration function, if available. If the previous tasks were sufficient to meet the low threshold value that is coded in the SG where the volume resides, or the value that is specified in the DFSMShsm PARMLIB member ARCCMDxx, the space management ends for that volume, and the next volume is selected for processing. Otherwise, DFSMShsm continues primary space management processing. The next steps in primary space management are selecting and migrating the largest data set that is eligible for migration in the selected volume. All of the data sets are migrated to ML1 DASD, or ML2 tape, according to management class (MC) polices or ARCCMDxx
specifications. Migration processing moves to the next volume when either of these conditions is met: Volume met the low threshold utilization that is coded in the SG, or no more data sets are eligible for migration. In a non-SMS environment, all data sets that are eligible are migrated, regardless of the volume space usage.
A data set that is migrated from a non-SMS-managed volume can be recalled to an
SMS-managed volume if SMS is active and if the data set meets the conditions for selecting SMS management for that data set. DFSMShsm recalls a non-SMS-managed data set to a non-SMS-managed volume only if the data set does not meet the conditions to become an SMS-managed data set, or if a command forces the recall to a non-SMS-managed volume. DFSMShsm-managed volumes are usually defined in SMS storage groups.
Non-SMS-managed volumes can be defined directly in the ARCCMDxx member in DFSMShsm PARMLIB. DFSMShsm performs space management on both SMS-managed and non-SMS-managed volumes.
1.6.3 Secondary space management
In secondary space management, in addition to moving data sets from ML1 volumes to ML2 volumes, DFSMShsm performs migration cleanup. These processes are performed in parallel. Migration cleanup deletes expired data sets, erases deleted data from SDSP data sets, and deletes unwanted records from the DFSMShsm MCDS.
DFSMShsm also performs these tasks:
Schedules TAPECOPY commands for migration tape copy-needed (TCN) records
Deletes expired data sets from the migration volumes
Deletes obsolete MCDs, volume statistics records (VSRs), and DSRs during migration cleanup
Moves data sets (under the control of the management class) from ML1 to ML2 volumes
1.6.4 Interval migration
DFSMShsm interval migration ensures that a specified amount of space is available on an hourly basis. DFSMShsm performs interval migration, as needed, for all storage groups that are eligible for interval management. In interval migration, DFSMShsm performs a space check on each DFSMShsm volume that is being managed. A volume is considered eligible for interval migration based on the AUTOMIGRATE (AM=) and THRESHOLD settings of its storage group.
Chapter 1. DFSMShsm overview 13
When AM=I, the space that is used must exceed the halfway mark between high and low thresholds to make the volume eligible. When AM=Y, the space that is used must exceed the high threshold to make the volume eligible. DFSMShsm migrates eligible data sets to ML1 or ML2 volumes. This process continues until the volume that is managed by DFSMShsm reaches the low threshold or no more data sets are eligible.
1.6.5 On-demand migration
On-demand migration is available as an alternative to interval migration. On-demand migration performs near immediate space management on eligible SMS-managed volumes that exceed the specified volume high threshold, instead of waiting for interval migration to run at the top of each hour. On-demand migration migrates data sets to ML1 or ML2 volumes and continues to process the volume until the low threshold is reached or no eligible data sets remain.
On-demand migration is based on an event notification from SMS. You can configure your system to manage your space needs.