Customizing IBM Tivoli Workload Scheduler for z/OS V8.2 to Improve Performance

80 Customizing IBM Tivoli Workload Scheduler for z/OS V8.2 to Improve Performance

Figure 4-11 zFS in a colony address space

4.3.5 zFS aggregates

A zFS aggregate is a data set that contains zFSs. The aggregate is a VSAM

Linear Data Set (VSAM LDS) and is a container that can contain one or more

zFS. An aggregate can only have one VSAM LDS, but it can contain an unlimited

number of file systems. The name of the aggregate is the same as the VSAM

LDS name.

Sufficient space must be available on the volume or volumes, because multiple

volumes can be specified on the DEFINE of the VSAM LDS. DFSMS decides

when to allocate on these volumes during any extension of a primary allocation.

VSAM LDSs greater than 4 GB can be specified by using the extended format

and extended addressability capability in the data class of the data set. For

allocation of VSAM data sets for zFS aggregates, see “Allocating a zFS” on

page 84.

After the aggregate is created, formatting of the aggregate is necessary before

any file systems can exist in it. A zFS is a named entity that resides in a zFS

aggregate. It contains a root directory and can be mounted into the USS

hierarchy. Although the term file system is not a new term, a zFS resides in a zFS

aggregate, which is different from an HFS.

Chapter 4. Optimizing the UNIX System Services environment 81

zFS aggregates come in two types:

 Compatibility mode aggregates

 Multiple file system aggregates

Compatibility mode aggregates

A compatibility mode aggregate can contain only one zFS, making this type of

aggregate more like an HFS. This is flagged in the aggregate when it is created.

The name of the file system is the same as the name of the aggregate, which is

the same as the VSAM LDS cluster name. The file system size (called a quota) in

a compatibility mode aggregate is set to the size of the aggregate. Compatibility

mode aggregates are more like an HFS data set, except that they are VSAM

linear data sets instead of HFS data sets. We recommend that you start using

compatibility mode aggregates first, because they are more like the familiar HFS

data sets. Figure 4-12 shows a compatibility mode aggregate.

Figure 4-12 zFS compatibility mode aggregate

Multiple file mode aggregates

A multi-file mode aggregate enables the administrator to define multiple zFSs in

a single aggregate. This type of aggregate can contain one or more zFSs. This

allows space that becomes available when files are deleted in one file system to

be made available to other file systems in the same aggregate data set or space

sharing.

82 Customizing IBM Tivoli Workload Scheduler for z/OS V8.2 to Improve Performance

Space sharing

Space sharing means that if you have multiple file systems in a single data set,

and files are removed from one of the file systems, which frees DASD space,

another file system can use that space when new files are created. This new type

of file system is called a multi-file-system aggregate.

The multiple file system aggregate OMVS.EBIS.zFS, shown in Figure 4-13, can

contain multiple zFSs. This makes it possible to do space sharing between the

zFSs within the aggregate.

The multiple file system aggregate has its own name. This name is assigned

when the aggregate is created. It is always the same as the VSAM LDS cluster

name. Each zFS in the aggregate has its own file system name. This name is

assigned when the particular file system in the aggregate is created. Each zFS

also has a predefined maximum size, called the quota.

Figure 4-13 zFS multiple file mode aggregates

Metadata cache

The zFS has a cache for file system metadata, which includes directory contents

and the data of files that are smaller than the aggregate block size. The setting of

this cache size is important to performance because zFS references the file

system metadata frequently.