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README.CCKD64.md

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Hercules CCKD64 Support

Contents

  1. About CCKD64
  2. Conversion to CCKD64
  3. Procedure
  4. Additional Information

About CCKD64

Version 4.2 of SDL Hercules Hyperion introduced support for very large Compressed CKD (CCKD) dasd image files, called CCKD64, which can be much larger than 4GB in size.

The current default implementation of CCKD only supports a maximum file size of 4GB. With the current CCKD implementation, when a compressed CCKD dasd image file (or any of its associated shadow files) reaches a file size of 4GB, unrecoverable I/O errors occur. This is caused by the use of only 32-bit file offset values being used in the original design.

With the introduction of CCKD64 support however, the new CCKD64 file format uses 64-bit file offsets, thus allowing CCKD64 format compressed dasd image files (and their associated shadow files) to grow to the theoretical maximum of 18EB in size. (The actual maximum size that any operating system file can actually be however, is limited by the operating system itself as well as the format of the file system that the file resides on. On Windows with NTFS volumes for example, the actual maximum supported file size is 16TB.)

Conversion to CCKD64

In order to take advantage of the new CCKD64 file format, existing emulated dasd image files in the old CCKD compressed format must first be converted to the new CCKD64 format by either:

  • Using the new convto64 utility to individually convert each old format base image and associated shadow files to the new format (recommended), or

  • Creating brand new cckd64 base image file using the new dasdinit64 utility, or

  • Copying existing old format CCKD images to the new CCKD64 format using the new dasdcopy64 utility.

It is critical the dasd images being converted not have any errors before they are converted! It is therefore highly recommended that cckdcdsk -3 be run on each image before they are converted.

Using the convto64 utility to convert existing CCKD files to the CCKD64 format is recommended over using dasdcopy64 as it is not only significantly faster than dasdcopy64 but is also able to convert individual CCKD shadow files as well (which dasdcopy64 cannot currently do). That is to say, if you already have a CCKD format base dasd image file with one or more shadow files associated with it, dasdcopy64 can only copy the base image plus all of its shadow files into a single new CCKD64 base image file (i.e. the shadow files are automatically merged during the copy operation, resulting in a single CCKD64 base dasd image output file).

The convto64 utility however, directly converts base images -OR- shadow files individually, resulting in a new CCKD64 format base image or shadow file. It does not "merge" them together. Plus, as previously mentioned, it is significantly faster than dasdcopy64 too. It is therefore the recommended way to convert existing CCKD dasd images (and shadow files) to the new CCKD64 format.

Procedure

  1. Run cckdcdsk -3 on all existing 32-bit CCKD dasds to correct any existing errors. (Critical!)

  2. Use convto64 to individually convert all 32-bit CCKD base images and associated shadow files to the new 64-bit CCKD64 format. Please note that each shadow file and base image must each be converted separately. (required!)

  3. Run cckdcdsk64 -3 -ro on all of the newly converted 64-bit CCKD64 dasd images to verify the conversion was successful and that no errors exist on any of the images. (optional)

Additional Information

In addition to the new dasdinit64 and dasdcopy64 utilities, there are also corresponding CCKD64 versions of:

cckdcdsk check disk utility called cckdcdsk64
cckdcomp compression utility called cckdcomp64
cckdswap endianness toggling utility called cckdswap64
cckddiag diagnostic utility called cckddiag64
dasdconv conversion utility called dasdconv64
dasdload dasd building utility called dasdload64

The existing dasdls, dasdcat, dasdpdsu, dasdisup, and dasdseq utilities do not have any specialized CCKD64 versions. However, all of them do support the new CCKD64 file format in addition to the existing CCKD file format. They just don't have separate executable names ending in '64', since they have all been updated to support either of the two formats automatically.

Additional information regarding the new CCKD64 file format can be found on the Compressed Dasd Emulation web page.