The storage group and management class are interrelated. The storage group Auto Migrate and Auto Backup parameters specify whether the volumes in this storage group are eligible to be processed automatically. The management class, assigned to the data sets residing on the volumes, determines whether and how to process the data sets on the volume. In contrast, if you set Auto Migrate or Auto Backup to N (No) in the storage group, the volumes in the storage group are not processed and data sets residing in the storage group are not migrated or backed up.
You can specify the following attributes on the Pool Storage Group Define panel:
DFSMShsm ignores storage groups for which you specify a different system name, and does not process DASD volumes that have already been processed. Do not specify a Sys/Sys Group Name unless processing of the storage group for the function must be performed only on that one host because that limits the capabilities of DFSMShsm to perform the request.
The same rules apply to Backup Sys/Sys Group Name for data availability management processing, and to Dump Sys/Sys Group Name for automatic dump processing. All three Sys/Sys Group Name fields are optional and primed with blanks.
To make overflow storage groups eligible for allocation, you must assign designated overflow storage groups in your storage group ACS routine.
If all volumes in a non-overflow storage group are so full that the current allocation request will push them over high threshold, while volumes in the overflow storage group are not so full, then the new data set will be allocated on a volume in the overflow storage group. The assumption is that all other attributes of the non-overflow storage group and overflow storage group and the volumes in those storage groups are the same.
During initial allocation, volumes in an overflow storage group are less preferred than volumes in an enabled storage group but more preferred than volumes in a quiesced storage group. Therefore, overflow volumes are not placed on the primary volume list but can be placed on the secondary volume list. When an overflow storage group contains more volumes than a non-overflow storage group, specified volume counts might result in overflow volumes being preferred over volumes in the non-overflow storage group.
An overflow storage group may also be specified as an extend storage group.
Volumes residing in overflow storage groups are preferred over quiesced volumes and storage groups. If you quiesce an overflow storage group or volume then the quiesced volumes are preferred over quiesced overflow volumes.
Extend SG Name is an optional field of one-to-eight alphanumeric or national characters, or a combination, the first of which must be alphabetic. ISMF primes the field with the default value "blank."
You can define only one extend storage group to each storage group. However, you can define the same extend storage group to more than one primary storage group. Also, you can define two storage groups as extend storage groups of each other.
An extend storage group may also be specified as an overflow storage group.
Extend storage groups will not be used for initial allocation unless they are specified in the ACS routines. All storage groups that are listed in the ACS routines are candidates for initial allocation. Extend storage group attributes are not referenced during initial allocation.
For more information about data set extend in the volume selection process, see SMS volume selection for data set allocation.
You can specify the name of a copy pool backup storage group that is shared by more than one pool storage group.
Copy Pool Backup SG Name is an optional field of one-to-eight alphanumeric or national characters, or a combination, the first of which must be alphabetic. ISMF primes the field with the default value of a blank name.
When DFSMShsm dumps DASD volumes that belong to the storage group, it directs their contents to the dump classes. To use dump classes, you must first define their names and parameters using DFSMShsm. Then you can identify the dump class names to SMS using this panel.
Dump Class is an optional field. ISMF primes the field with the default value "blank."
SMS tries to stay within these thresholds by looking at the primary space allocation of each data set before assigning it to a given DASD volume. For example, the SMS volume selection function attempts to prevent allocation of a data set to a given DASD volume if that allocation causes the volume's high threshold to be exceeded. When a volume reaches or exceeds the high threshold, SMS issues an ENF72 signal, regardless of the Auto Migrate setting.
In addition, this high threshold value is used by DFSMShsm to determine whether data sets should be migrated off a DASD volume in the storage group. The low threshold value is used as the threshold goal in reducing the amount of space occupied on a DASD volume in the storage group during interval migration or daily space management. The low threshold value must be less than or equal to the high threshold value.
Both numbers are percentages of the total space on the DASD volume. If you specify Y for Auto Migrate, then you must specify both a high and low threshold. If you specify Y, the low threshold limit is 1. If you specify I for automatic interval migration, you can specify a low threshold value of 0 to migrate all the data sets in the selected storage group. The hourly migration trigger for storage groups with a value of AM=I is the occupancy at or above the midpoint of the high and low thresholds. Because storage groups used for tape mount management tend to fill up several times a day, allowing interval migration for these storage groups allows DFSMShsm to better keep up with the demand.
ISMF requires that you enter a high threshold value when you specify N for Auto Migrate, when defining a pool storage group. Because SMS needs the value for allocation purposes, the High Threshold field is a required field with a primed value of 85.
For a track-managed space of an extended address volume, the allocation and migration threshold specifies the threshold percentage of space allocation that triggers or stops migration of data sets from volumes in this storage group during interval migration. Valid values for high threshold are 1-100. Valid values for low threshold are 0-99. These fields are primed with default values and are ignored by SMS and DFSMShsm for other than extended address volumes. For the default values, refer to the ISMF help. If you alter an existing storage group to add extended address volume values, the specified bits are set to ON, when you specify the BreakPointValue and the Track Allocation Thresholds. If the specified indicators are not ON, SMS uses the existing threshold values, which represent threshold values for the entire volume, to represent threshold values for the track-managed space.
For more information about specifying allocation and migration thresholds, see z/OS DFSMShsm Storage Administration.
For more information about selecting appropriate threshold levels, see z/OS DFSMS Implementing System-Managed Storage.
You specify the maximum number of days that can elapse between backups. You can specify from 1 to 9999 days or you can specify NOLIMIT. If you specify NOLIMIT, then data sets in the storage group are backed up according to management class specifications. There is no default.
BreakPointValue applies only to data sets that are EAS (Extended Addressing Space)-eligible. Data sets that are not EAS-eligible must reside in the track-managed region of a volume.
When a disk space request is equal to or greater than the value for BreakPointValue, the system prefers to use the cylinder-managed space for that extent. If not enough cylinder-managed space is available, the system uses track-managed space or both cylinder-managed space and track-managed space. If the requested disk space is less than the value for BreakPointValue, the system prefers to use track-managed space. If not enough track-managed space is available, the system uses cylinder-managed space or both track-managed space and cylinder-managed space.
BreakPointValue is optional. If it is not specified for the storage group, the system uses the default value specified in the IGDSMSxx member of SYS1.PARMLIB, or a value of 10 cylinders if no BreakPointValue is specified in IGDSMSxx.