IBM DS8000 manual Dynamic Parallel Access Volumes required for large volumes

Note that some data set types cannot grow beyond 64K tracks. When coming from 3390-3 and staying with 50,085 tracks of a model 3 this limit of 64K tracks extent allocation is not an issue. When you already work with larger volumes you are familiar with these considerations. But it may be a surprise to you without this experience.

Data set types that can exploit more than 64K tracks are:

￿Physical sequential extended format, DSORG=PSE

￿VSAM

￿PDSE

￿HFS

￿Page data sets

Note that extended format data sets are required to reside on system-managed volumes. The extended format attribute is usually assigned through a data class construct. Example 14-1displays a list of data classes which have the extended attribute.

Example 14-1 Data Classes with EF attribute

DATA CLASS LIST

Command ===>

CDS Name : SYS1.DFSMS.SCDS

Enter Line Operators below:

LINE	DATACLAS	LAST TIME		EXTENDED
OPERATOR	NAME	MODIFIED	DATA SET NAME TYPE	ADDRESSABILITY	COMPACTION
---(1)----	--(2)---	--(25)---	-------(26)-------	-----(27)-----	---(28)---
	EXT	10:45	EXTENDED REQUIRED	YES	NO
	EXTCOMP	07:30	EXTENDED REQUIRED	YES	YES
	STRIPE	06:59	EXTENDED REQUIRED	NO	----
	XRCJ	07:09	EXTENDED REQUIRED	NO	----
----------	--------	--------	---------- ---------- BOTTOM OF		DATA --------

Data set types that cannot grow beyond 64K tracks are:

￿Physical sequential, DSORG=PS

￿Partitioned, DSORG=PO

￿Direct, DSORG=DA

￿JES spool

Data set types that must be allocated in the first 64K tracks on the volume are:

￿VTOC

￿VTOC Index

￿JES spool without APAR OW49317

Furthermore, consider adjusting the VTOC size when moving to large volumes. It all depends on the number of data sets allocated on the volume. You might consider defining the same size for VTOC, VTOC Index, and VVDS for all volumes with the same capacity, although the sizing requirements for database volumes are usually different than for TSO volumes. There are some further recommendations in Device Support Facilities User’s Guide and Reference, Release 17, GC35-0033-27, Appendix C. VTOC Index, and in the following sections.

Dynamic Parallel Access Volumes required for large volumes

Utilizing big volumes will require you to use dynamic Parallel Access Volumes (PAV) to allow many concurrent accesses to the very same volume concurrently. On a big volume, with

9 times the capacity of a 3390-3, we see about 9 times as many concurrent I/Os as what we

296DS8000 Series: Concepts and Architecture