Compressed
SPD Engine data sets occupy blocks of space on the disk. The size of a
block is derived from the IOBLOCKSIZE= data set option specified when the data set is created.
When the data set is updated, a new block fragment might need to be created to hold
the update. More updates might then create new fragments, which, in turn, increases
the number of
I/O
operations needed to read a data set.
By increasing the block padding in certain situations where many updates to the data
set are expected, fragmentation
can be kept to a minimum. However, adding padding can waste space if you do not update
the data set.
You must weigh the cost
of padding all compression blocks against the cost of possible fragmentation
of some compression blocks.
Specifying the PADCOMPRESS=
data set option when you create or update a data set adds space to
all of the blocks as they are written back to the disk. The PADCOMPRESS=
setting is not retained in the data set's metadata.