VTOC SELECT Statement

VTOC SELECT statement syntax

SELECT	***VTOC
	,POS=BEGIN\|END\|KEEP\|MIDDLE\|cccchhhh
	,SIZE=nnnnn

VTOC SELECT statement

This statement is similar in function and use to the SELECT statement, but applies only to the VTOC. You may use it to change the size and/or position of the VTOC. It may also appear as part of a sequenced set, under a SEQUENCE statement, in which case the POS= operand must be omitted; in this case the sequence set defines the data sets that immediately precede and/or follow the VTOC. A SELECT ***VTOC can ONLY be specified with COMPAKT-from-backup (TYPE=CPK) and the VTOC=COMPAKT operand MUST also be specified.

VTOC SELECT statement operands

***VTOC

This is a required operand and identifies this SELECT statement as applying to the VTOC.

POS=

Specifies the new position of the VTOC.

BEGIN

You desire the VTOC to be as near to the beginning of the DASD volume as possible.

END

You desire the VTOC to be as near to the end of the DASD volume as possible.

KEEP

The VTOC is to retain its position.

MIDDLE

You wish COMPAKTOR to position the VTOC as near the center of the DASD volume as possible.

cccchhhh

If you desire to position the VTOC at a specific location, code an 8-digit decimal number. The first 4 digits being the cylinder address, the last 4, the track address. Both addresses must be relative to zero. POS=00000000 is invalid. CPK fails if the new position of the VTOC overlaps an unmovable data set or another absolute positioned data set

On a DASD volume with over 65,535 tracks (such as the 3390-9 or an EAV) the last track of the VTOC must be no higher than relative track 65,535 (cylinder 4368, track 14 on a 3390-9).

If omitted, the default action is to retain the position of the VTOC, unless this statement appears in a sequenced set (see SEQUENCE in Section 40.11 “SEQUENCE and ENDSEQ Statements”).

Important

On modern cached and RAID DASD subsystems, the position of the VTOC is not as important for performance as it once was, so we recommend VTOCs be placed at the beginning of each volume. For ABR customers, data sets archived from volumes whose VTOCs are located at relative track 32767 or above, Auto-Recall may not work properly in all cases.

SIZE=

nnnnn

If coded, supply 1 to 5 decimal digits giving the VTOC size in tracks. A value of 0 is invalid, as is a value in excess of the device capacity. CPK fails if the expanded VTOC overlaps an unmovable data set or an absolute positioned data set. If you reduce the size of the VTOC, make sure that it is large enough to hold all current active DSCBs. If not, COMPAKTOR terminates.

If omitted, the VTOC retains its original size.

Notes on VTOC positioning

When changing the location of the VTOC, consider the following:

On current-technology DASD volumes, with their fast access and cache, you may wish to place the VTOC at the beginning of the volume.

Place the VTOC in such a manner that its last track is also the last track of a cylinder, that is, the VTOC ends on a cylinder boundary. This may also improve performance. When a VTOC is relatively positioned, as with POS=MIDDLE, POS=BEGIN, or POS=END, COMPAKTOR always places the VTOC to end on a cylinder boundary. This is also true when the VTOC is part of a sequenced set.