value of “1” forces the use of ZLIB compression. A value of “2” forces the use of
BZIP2 compression. The default is “1”.
LEVEL=
The LEVEL option controls the level of compression. It ranges from “1” (for fastest
compression) to “9” (for best compression). The default compression level is “4”.
CHUNKSIZE=
The CHUNKSIZE option allows you to create HET files with different chunk sizes.
The AWSTAPE (and therefore HET) formats allow each tape block to be logically
broken up into smaller chunks. For instance, if the S/3x0 application creates tapes
with a block size of 27998, those blocks would be broken down into nnnnn sized
chunks. Although possible it is not recommended to change the chunk size, as de-
creasing this may reduce compression performance. The range of nnnnn is from
4096 to 65535. 65535 is the default.
STRICTSIZE=
Upon reaching the tape file size limit, depending on strictsize, the tape file will or
will not be truncated to enforce the maxsize limit. The limit is only enforced during a
write type operation. If the file already exists and the program only reads the file,
then the file will not be truncated, regardless of the strictsize setting.
This affects any write that starts below the limit, but that would extend beyond the
limit. The strictsize parameter only affects compressed HET files. On AWS tapes,
the limit is always enforced, but the file is not truncated (the write does not occur,
because first AWS tapes are never truncated and second the effects of the write
are known in advance).
Regardless of strictsize, any write operation (Write, Write TM) will return a Unit
Check with Equipment Check to the program if the file size exceeds the predefined
limit. If strictsize is “0”, the write will actually have been performed on the tape file.
When strictsize is set to “1”, the file will be truncated on the preceding tape block
boundary.
Care must be taken that regardless of the strictsize setting, the tape may become
unusable for the guest program should such an event occur (absence of a Tape
Mark for example). This option has no effect if maxsize is 0. The default is “0” (do
not truncate).
The remaining parameters are described in section
FakeTape virtual files”).
6.8.4.4 Examples
Example 1:
Define a 3490 tape device on device address 0580. The tape device is a HET virtual file with name
"R0674A.HET" located in path "/S390/TAPES/". BZIP2 compression has to be turned on at a level of 9
(best compression).
0580 3490 /S390/TAPES/R0674A.HET COMPRESS=1 METHOD=2 LEVEL=9
Example 2:
Define a 3490 tape device on device address 0580. The tape device is a HET virtual file with name
"R0675A.HET" located in path "/S390/TAPES/". Mount the tape as read/write.
0580 3490 /S390/TAPES/R0675A.HET RING
