The VSS3OPTIMIZE option supports 4096-byte physical sector disks.

The VSS3OPTIMIZE option, when set to TRUE, aligns structures on block boundaries that are multiples of 660 words. The specified BLOCKSIZE option value must be a multiple of 22 segments.

For existing structures that use the default blocking attributes of DASDL, setting VSS3OPTIMIZE to TRUE, automatically reorganizes for VSS-3 optimization.

Setting VSS3OPTIMIZE to FALSE ignores existing structures that are not optimized. Setting VSS3OPTIMIZE to FALSE does not “unoptimize” a structure.

The VSS2OPTIMIZE and VSS3OPTIMIZE options are mutually exclusive. VSS3OPTIMIZE structures are aligned on block boundaries that are multiples of 660 words, while VSS2OPTIMIZE structures are aligned on block boundaries that are multiples of 60 words. If both the VSS2OPTIMIZE option and VSS3OPTIMIZE option are specified at the same level, DASDL produces a syntax error.

New structures (whether created as part of new databases or added to existing databases) are not, by default, automatically optimized for VSS-3. This differs from the VSS2OPTIMIZE option. The VSS3OPTIMIZE default applies to existing structures and is FALSE.

The VSS3OPTIMIZE option cannot be specified for a set with a defined block size that is not a multiple of 22 segments.

When both the VSS3OPTIMIZE and BLOCKSIZE options are specified, the DASDL compiler uses them to calculate the optimal block size in words.If the calculation results in wasting more than one segment (30 words), the DASDL compiler will ignore the VSS3OPTIMIZE option. To preserve the VSS3OPTIMIZE option, users can either remove the BLOCKSIZE option, add a new filler item or expand an existing filler item.

For an existing structure, changing the block size requires a file format conversion reorganization.