1. IEBCOPY obtains as large a work area as possible, up to the value of the WORK parameter.
2. An initial minimum sized buffer and channel program construction area is allocated from the work area.

   The size of this area is approximately 4 times the size of the largest input or output device track, plus about 3%.

   If IEBCOPY cannot allocate a minimum sized work area, it will stop with a message.

3. IEBCOPY processes control statements, reads the partitioned data set directories, and builds a table of members to be copied. When the work area cannot hold the table and all directories, the directory entries are spilled to SYSUT3 and SYSUT4 to allow the table to grow. When no room remains and all directories are spilled, then IEBCOPY ends with a message.
4. If enough storage remains unused in the work area, it is used as a second buffer.

   If a SIZE= parameter is specified, the size of the second buffer is limited so that the total size of both buffers does not exceed the specified value. If the SIZE= value will not allow a minimum sized second buffer, it is not allocated.

Tip: When SIZE=999999 (or any number that is a few thousand less than the WORK= value) is coded, IEBCOPY might be able to allocate buffers in the work area but not have enough room remaining for tables. If this happens, increase the REGION= and WORK= values, or remove the SIZE= parameter.

When data sets with huge directories are copied, make the largest amount of virtual storage available to retain directory information. Specify WORK=8M (or another large value) and a correspondingly large REGION.

When data sets with small directories are copied with large work area sizes, the second I/O buffer can become very large (megabytes) and cause real storage shortages. This could result in increased system paging and system sluggishness, because most of the buffer is backed by real frames which are fixed for duration of the I/O. In this case, specify SIZE=1M or a smaller value to limit the amount of storage used for buffers, but allow lots of storage to be used for directory information.