You must configure what storage DFSMShsm manages and how much space to free on the volumes. This configuration specification comes from the storage group that the volume belongs to.
You can use the Auto Migrate attribute to specify whether DFSMShsm performs primary space management and event-driven migration on the volumes that are assigned to the storage group. The Auto Migrate attribute specifies the type of space management that DFSMShsm uses on the volumes that are assigned to the storage group. Table 1 lists the acceptable values of the Auto Migrate attribute and the space management methods that are performed based on those values.
| Auto Migrate (AM) Value | Primary Space Management Performed? | Interval Migration Performed? | On-demand Migration Performed? |
|---|---|---|---|
| Y (yes) | Yes | Yes1 | Yes2 |
| I (interval) | Yes | Yes | No |
| P (primary) | Yes | No | No |
| N (no)3 | No | No | No |
| Notes:
|
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A storage group defined with AM=Y indicates that you want the storage group space managed by primary space management, and, on occasion, by event-driven migration. If the setting SETSYS INTERVALMIGRATION is specified, volumes that belong to the storage group are eligible for interval migration. If the setting SETSYS ONDEMANDMIGRATION(Y) is specified, volumes that belong to the storage group are eligible for on-demand migration and are not eligible for interval migration, even if SETSYS INTERVALMIGRATION is specified. Specific interval migration or on-demand migration requirements must be satisfied for a volume to be eligible.
A storage group defined with AM=I indicates that you want the storage group space managed by interval migration. Primary space management can also be performed, but plays a minor role overall. Processing of a storage group defined with AM=I by interval migration is not affected by the SETSYS INTERVALMIGRATION or SETSYS NOINTERVALMIGRATION settings that apply to storage groups that are defined with AM=Y. Defining a storage group with AM=I is ideal for use with tape mount management (TMM), which redirects tape data sets to the storage group, and then lets DFSMShsm move them to tape hourly, as needed.
AM=I storage groups also have a different trigger for interval migration to be performed. That is, when a volume exceeds the midpoint between low and high threshold, interval migration is performed. For example, if low threshold is 20 percent and the high threshold is 70 percent, then volumes that exceed 45 percent are processed.
A storage group defined with AM=P indicates that you want the storage group managed by primary space management only. This is useful when event-driven migration is determined to consume too much resource or is disruptive in other ways. Processing of a storage group defined with AM=P by primary space management is not affected by the SETSYS INTERVALMIGRATION or SETSYS ONDEMANDMIGRATION settings that apply to storage groups defined with AM=Y.
A storage group defined with AM=N indicates that you do not want automatic space management to be performed. Data sets and volumes must be migrated using commands instead. Defining a storage group with AM=N is ideal when the volumes are managed by other products or when you do not want space management performed (such as for application database or system volumes that must remain DASD-resident for other reasons).
In Figure 1, primary space management is performed on storage groups SG1 and SG2 (although event-driven migration is also performed on these storage groups). Interval migration is performed on storage group SG3. Storage group SG4 is not space managed, but has thresholds to control new data set allocation.
NAME ===> SG1
MIGRATE SYSTEM/SYSPLEX NAME ===>
AUTO MIGRATE ===> Y
MIGRATION AND ALLOCATION THRESHOLDS: HIGH ===> 85 LOW ===> 70
NAME ===> SG2
MIGRATE SYSTEM/SYSPLEX NAME ===>
AUTO MIGRATE ===> Y
MIGRATION AND ALLOCATION THRESHOLDS: HIGH ===> 95 LOW ===> 80
NAME ===> SG3
MIGRATE SYSTEM/SYSPLEX NAME ===>
AUTO MIGRATE ===> I
MIGRATION AND ALLOCATION THRESHOLDS: HIGH ===> 20 LOW ===> 0
NAME ===> SG4
MIGRATE SYSTEM/SYSPLEX NAME ===>
AUTO MIGRATE ===> N
MIGRATION AND ALLOCATION THRESHOLDS: HIGH ===> 95 LOW ===> 80
Pass 1 of automatic primary space management (non-data-movement function in primary space management) and extent reduction are performed for all volumes in storage groups defined with AM=Y and AM=I (SG1, SG2, and SG3). Pass 2 of automatic primary space management (migration) is performed only for those volumes that are above the low threshold after pass 1 and extent reduction have completed.
SMS tries to stay within these thresholds by assessing the primary space allocation of each data set before assigning it to a given DASD volume. When a volume reaches or exceeds the high threshold, SMS issues an ENF72 signal, regardless of the Auto Migrate setting. This event code is the trigger for on-demand migration.
DFSMShsm uses the high threshold attribute to determine the need for event-driven migration. The low threshold attribute specifies the maximum level of occupied space after space management is performed.
Space management is considered complete when both thresholds have been met. This applies only to interval migration of non-SMS-managed volumes and event-driven migration of SMS-managed volumes when Auto Migrate is not I. Interval migration of SMS-managed volumes that belong to a storage group defined with AM=I is performed if the volume is at or above the midpoint between the low and high threshold.