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Reference Guide › Configuration File Reference › SUBPOOL Record

SUBPOOL Record

Use the SUBPOOL record to define a CA VM:Director subpool and specify how CA VM:Director allocates disk space from it.

SUBPOOL name {"Method"} {HIGHEND | LOWEND} maxspace [EXPLICIT]

Method:

  ROTATING
| LINEAR
| LARGEGAP
| SMALLGAP [nK | nM]

Configuration File

SUBPOOL is defined in the DASD CONFIG file.

Definitions

name

Specifies a unique name that identifies the subpool you are defining.

ROTATING

Allocates disk space to minidisks in a first fit fashion across all volumes having extents in the subpool. CA VM:Director allocates the first minidisk on the first volume that has an extent in the subpool with sufficient space for the minidisk. It allocates the second minidisk on the next volume that has an extent in the subpool with sufficient space for the minidisk, and so on. The HIGHEND | LOWEND parameters determine allocations within an extent on a volume.

LINEAR

Allocates disk space to minidisks in a first fit fashion, from the first volume that has an extent in the subpool with sufficient space for the minidisk. CA VM:Director searches the volumes in reverse order of their definition in the DASD CONFIG file. It allocates subsequent minidisks to the same volume until its extents that are in the subpool are full or the required space is not available. Then CA VM:Director uses the next volume that has extents in the subpool. The HIGHEND | LOWEND parameters determine allocations within an extent on a volume.

SMALLGAP [nK | nM]

Allocates disk space to minidisks in a best fit fashion from the smallest gap of available space on any volume that has an extent in a subpool. CA VM:Director searches volumes in reverse order of their definition in the DASD CONFIG file. It repeats the search for a best fit for each subsequent minidisk allocation. If you specify the nK parameter, then the gap must be large enough for the minidisk you request and the amount of additional disk space you specify with this parameter. CA VM:Director only tests for this minimum amount of remaining space if it cannot locate a gap in the subpool that exactly matches the size of the requested minidisk. If you do not specify this parameter, CA VM:Director does not check for remaining space. Replace n with the number of kilobytes (K) or megabytes (M) you want remaining in the gap after CA VM:Director allocates a minidisk you request. Replacing n with zero is the same as not specifying the parameter.

The best fit is always an exact match in size between the requested disk space and an available gap. If CA VM:Director cannot find an exact match, it looks for the next best fit which is the smallest gap that has sufficient available space. If two or more locations in a single extent satisfy the best fit criteria, then the HIGHEND | LOWEND options determine which one CA VM:Director uses. If no gaps are large enough to allocate the requested space and leave the required minimum amount of space remaining, the allocation reverts to LARGEGAP rules. Thus, the largest amount of disk space possible remains after the allocation.

Note: SMALLGAP and LARGEGAP can sometimes help reduce the amount of fragmentation and the number and frequency of COMPRESS runs.

LARGEGAP

Allocates disk space to minidisks in a best fit fashion from the largest gap of available space on any volume that has an extent in a subpool. CA VM:Director searches volumes in reverse order of their definition in the DASD CONFIG file. It repeats the search for a best fit for each subsequent minidisk allocation.

The best fit is always an exact match in size between the requested disk space and an available gap. If CA VM:Director cannot find an exact match, it looks for the next best fit which is the largest gap that has sufficient available space. If two or more locations in a single extent satisfy the best fit criteria, then the HIGHEND | LOWEND options determine which gap CA VM:Director uses.

Note: SMALLGAP and LARGEGAP can sometimes help reduce the amount of fragmentation and the number and frequency of COMPRESS runs.

HIGHEND

Specifies that when CA VM:Director allocates disk space from any extent, the disk space should be as near the high end of the extent as possible.

Important! COMPRESS moves minidisks from the high end of an extent to the low end of the same extent.

LOWEND

Specifies that when CA VM:Director allocates disk space from any extent, the disk space should be as near the low end of the extent as possible.

maxspace | *

Specifies the maximum kilobytes (K) or megabytes (M) of disk space that CA VM:Director can allocate in a single request. If you specify an asterisk as the maximum amount of space, no limit is imposed.

This parameter lets you specify the maximum size of any minidisk in a subpool. If two subpools share the same extent but have different maxspace values, the minidisks allocated using one subpool can be larger than the minidisks allocated using the other subpool.

This parameter takes precedence over the limit parameter on the MANAGER record in the VMDIRECT MANAGERS file. If a directory manager has an allocation limit of 200M and the subpool maximum is 2K, the largest minidisk that CA VM:Director can define in that subpool is 2K.

[EXPLICIT]

Prevents CA VM:Director from searching this subpool during automatic allocation when using predefined subpool categories. All subpool categories respect the EXPLICIT attribute and ignore that subpool when searching for space.

Note: For more information about using subpool categories, see the Subpool Categories.

In a multiple CPU environment, a problem can occur if two systems try to allocate from the same disk space. If you use shared DASD, use the EXPLICIT parameter to prevent automatic allocation from a shared disk. This parameter gives you complete control over any allocations that CA VM:Director makes from those shared disks. You must specify the name of a subpool that is defined with the EXPLICIT attribute to have CA VM:Director allocate space from it.

Description

Each subpool definition specifies a method for allocating from extents and the maximum amount of disk space allowed for each allocation request.

CA VM:Director maintains a complete mapping of all controlled disk space within its virtual memory. Each time you define a minidisk, the subpool you specify governs where and how CA VM:Director will allocate the disk space.

In the DASD CONFIG file, a SUBPOOL record must appear before any EXTENT record that references the named subpool. You cannot continue SUBPOOL records beyond the first line.

To allow directory managers to use any individual subpools, authorize them specifically by including the subpool name on the MANAGER record in the VMDIRECT MANAGERS file.

Examples