Reference Guide › Command Reference › COMPRESS Command

COMPRESS Command

Use the COMPRESS command to reduce fragmentation of allocated disk space.

COMPRESS volser number subpool1 [subpool2 [limit]]

Definitions

volser

The volume serial number of the DASD containing the extent to compress.

number

The starting cylinder or block number of the extent to compress. This number is the same as the starting number defined on an EXTENT record in the DASD CONFIG file.

subpool1

The name of the subpool to use when allocating space within the extent being compressed. Choose a subpool that is valid for the extent being compressed that has a large allocation limit or no allocation limit.

subpool2

The name of the subpool from which to allocate space to hold the minidisk temporarily. The default name is the same as the subpool1 name.

limit

The number of 15‑second intervals to wait before bypassing a minidisk that is not available. The command waits if other virtual machines have links to a minidisk that needs to be moved. Before waiting, the command sends these users messages asking them to detach the link. The minimum number of wait intervals is 0; the maximum is 2147483647. The default is 10 intervals.

Description

The COMPRESS command reduces and controls excessive fragmentation of disk space that is under CA VM:Director management.

All minidisks within the extent are considered movable, provided the minidisk is not in use and moving or scratching the minidisk is not restricted by the optional SCRATCH user exit.

It does this by trying to move a minidisk from the high end of the extent to fill a free area at the low end of the extent. The COMPRESS command looks for a minidisk that exactly fits the free area first. If it cannot find a matching minidisk, it looks for a minidisk that can fit in the free area. If it cannot find a minidisk that fits in the free area, the command moves the minidisk immediately following the free area to a temporary area, then copies it from the temporary area to its new location in the free area.

The compression process continues until there are no more free spaces in the extent or until the remaining free space is concentrated in one free area. When the compression process is completed, the command formats all free space to erase any data left from a minidisk that was moved during the compression.

If you are compressing the extent where your own 191 minidisk resides, you must detach it before issuing the COMPRESS command. Any minidisk can be accessed temporarily as your A‑disk.

If a minidisk is in use, COMPRESS sends messages to the user ID to detach the minidisk or log off. If the user ID does not detach the minidisk or log off within the time limit, COMPRESS skips over the minidisk and continues the compression.

COMPRESS can move recomputed minidisks as long as there are no links to them. COMPRESS can move SQL minidisks as long as SQL is shut down and there are no links to the minidisks.

Examples

• You want to compress an extent on DASD volume USR01. The extent begins at block number 423000 and ends at block number 450000. The extent is located in subpool MAIN and you want to use the subpool TEMP for temporary minidisk storage, and you will wait 150 seconds for a minidisk that is not yet available (10 time intervals) before passing it. Enter the following command:

  vmdirect compress usr01 423000 main temp
  

  CA VM:Director responds:

  MOVING USER ‘ASTA’ MINIDISK ‘191’ TEMPORARILY TO VOLUME ‘USR02’
  MOVING USER ‘ASTA’ MINIDISK ‘191’ TO BLOCK 423000
  WAITING FOR USER ‘CINDY’ TO DETACH MINIDISK ‘191’
  WAITING FOR USER ‘CINDY’ TO DETACH MINIDISK ‘191’
  WAITING FOR USER ‘CINDY’ TO DETACH MINIDISK ‘191’
  MOVING USER ‘CINDY’ MINIDISK ‘191’ TEMPORARILY TO VOLUME ‘USR02’
  MOVING USER ‘CINDY’ MINIDISK ‘191’ TO BLOCK 425000
  FORMATTING 184 BLOCKS OF FREE SPACE AT BLOCK 425800
  THERE WAS A TOTAL OF 2 MINIDISK MOVES RESULTING IN 1 FREE AREA
  

• In the previous example, CA VM:Director waited for user ID CINDY to detach her 191 minidisk. To immediately bypass minidisks that need to be moved but which are currently linked, enter:

  vmdirect compress usr01 423000 main main 0
  

Note: For an explanation of extents, see the EXTENT Record.