Storage Classes Used in the Sample ACS Routines

The following list describes the storage classes used in the examples.

STANDARD

Assigned to most of your data sets that have average performance and availability requirements.

DFMCLASS

Assigned to data sets created by Distributed FileManager/MVS.

GSPACE

Lets the system programmer, database administrator, and storage administrator allocate data sets on specific volumes when required (for example, when data sets needed to recover a database should be allocated on a different volume than the one containing the database). It requires that specific volume requests are honored. It must be placed on the allocation request, because the ACS routine does not specifically assign the class.

NONVIO

Assigned to DFSORT temporary work data sets to prevent them from being written to VIO.

NONSMS

Used when creating data sets that should not be system-managed, and can only be used by system programmers, storage administrators, and database administrators. It is explicitly specified in JCL. The ACS routine must check for the NONSMS storage class and assign a null storage class.

MEDIUM

Assigned to CICS/VSAM and user database data sets that can benefit from the DASD fast write capability of a 3990 storage control with extended functions.

FAST

Assigned to DB2® and IMS™ production databases, IMS change accumulation logs and selected DL/1 databases. It is also assigned to CICS® user data sets, temporary storage, and production libraries, which require higher than average performance.

FASTREAD

Provides higher than average performance for data sets that are mostly read rather than written to. It must be specified on an allocation request, because the ACS routine does not specifically assign the class. This class can only be used by system programmers, storage administrators, and database administrators.

FASTWRIT

Assigned to the following test system database data sets that can benefit from the DASD fast write capability of the 3990 storage control with extended functions:

CICS intrapartition data set and selected CICS/VSAM databases
IMS write ahead and online log data sets, and scratch pad area
DB2 active log

DBCRIT

Assigned to database data sets that provide system definition and recovery support. It specifies that the data sets are to be allocated on dual copy volumes and use DASD fast write.

CRITICAL

Provides continuous availability and accessibility with better than average performance. It must be entered on an allocation request, because the ACS routine does not specifically assign the class. This class can only be used by system programmers, storage administrators, and database administrators.

MTLREMOT

Assigned to a tape data set allocation. It ensures that the data set is allocated to a remote system-managed manual tape library dataserver.

MTLSC

Assigned to a tape data set allocation. It ensures that the data set is assigned to a system-managed manual tape library dataserver.

ATLSC

Assigned to a tape data set allocation. It ensures that the data set is assigned to a system-managed automatic tape library dataserver.

Table 1 summarizes the attributes assigned to each storage class for the sample SMS ACS routines.

Table 1. Sample Storage Classes for Data Sets
Attributes	General Storage Classes
NAME	STANDARD	GSPACE	NONVIO	NONSMS
AVAILABILITY	STANDARD	STANDARD	STANDARD	STANDARD
ACCESSIBILITY	STANDARD	STANDARD	STANDARD	STANDARD
GUARANTEED SPACE	NO	YES	NO	NO
GUARANTEED SYNCHRONOUS WRITE	NO	NO	NO	NO
Attributes	High Performance Storage Classes
NAME	MEDIUM	FAST	FASTREAD	FASTWRIT
DIRECT MILLISECOND RESPONSE	10	5	5	5
DIRECT BIAS	—	—	R	W
SEQUENTIAL MILLISECOND RESPONSE	10	5	5	5
SEQUENTIAL BIAS	—	—	R	W
AVAILABILITY	STANDARD	STANDARD	STANDARD	STANDARD
ACCESSIBILITY	STANDARD	STANDARD	STANDARD	CONTINUOUS
GUARANTEED SPACE	NO	NO	NO	NO
GUARANTEED SYNCHRONOUS WRITE	NO	NO	NO	NO
Attributes	High Availability Storage Classes
NAME	DBCRIT	CRITICAL
DIRECT MILLISECOND RESPONSE	10	10
DIRECT BIAS	W	—
SEQUENTIAL MILLISECOND RESPONSE	10	10
SEQUENTIAL BIAS	R	—
AVAILABILITY	CONTINUOUS	CONTINUOUS
ACCESSIBILITY	CONTINUOUS	CONTINUOUS
GUARANTEED SPACE	YES	NO
GUARANTEED SYNCHRONOUS WRITE	NO	NO
Attributes	Additional Storage Classes
NAME	DFMCLASS	MTLREMOT	MTLSC	ATLSC
DIRECT MILLISECOND RESPONSE	5	—	—	—
SEQUENTIAL MILLISECOND RESPONSE	5	—	—	—
INITIAL ACCESS RESPONSE SECONDS	—	2	1	1
SUSTAINED DATA RATE	—	3	3	3
AVAILABILITY	STANDARD	STANDARD	STANDARD	STANDARD
ACCESSIBILITY	STANDARD	STANDARD	STANDARD	STANDARD
GUARANTEED SPACE	NO	NO	NO	NO
GUARANTEED SYNCHRONOUS WRITE	NO	NO	NO	NO

See SAMPLIB for the sample storage class ACS routine. This routine handles data set allocations on DASD and tape.

The routine first ensures that no storage class is assigned for data on devices not considered valid, for data on migration level 1 or 2 storage, for tape data, and for system data sets. Storage administrators and system programmers are also allowed to specify the NONSMS storage class during allocation, and this routine ensures that no storage class is assigned. These data sets are not system-managed.

Storage administrators, system programmers, and database administrators are allowed to assign any valid storage class.

Tape allocations that are assigned one of the tape mount management data classes are assigned either the STANDARD or NONVIO storage class:

STANDARD means there are no special performance attributes for tape devices.
Temporary DFSORT data sets are assigned the NONVIO storage class, which allows the storage group routine to assign the data to non-VIO storage. VIO tends to degrade DFSORT performance.

Next, the routine assigns storage classes to CICS, DB2, and IMS database data.

The DBCRIT storage class, used for dual copy, is assigned to selected CICS, DB2, and IMS data.
The FAST storage class, used for must-cache data, is assigned to selected CICS and IMS data.
The FASTWRIT storage class, used for DASD fast write, is assigned to selected CICS, DB2, and IMS data.
The MEDIUM storage class, used to provide better than average performance, is assigned to some CICS data.

All other CICS, DB2, IMS, and miscellaneous data sets are assigned the STANDARD storage class.

SAMPLIB also contains the sample storage class ACS routines for the temporary and permanent milestones.