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Because the CTTTPI utility thoroughly examines magnetic tapes in unknown condition, it may encounter more I/O errors than ordinary programs. In particular, CTTTPI encounters I/O errors when reading a new tape to which data has never been written. While CTTTPI handles most of these errors successfully, the user may observe pertinent error messages originated by the operating system. Normally these messages can be ignored. If automation procedures are driven by these messages, you can make adjustments to exclude tape initialization and media swapping jobs.
To minimize the overhead of I/O error recovery, CTTTPI turns off DDR/SWAP capability in the allocated device for a short duration while it reads the label of a mounted tape to be initialized. If CTTTPI is canceled during that short period, the device may be left in a state where it is not a candidate for DDR/SWAP.
The operator can increase control over DDR/SWAP using operating system commands G OFF and G ON.
Note: In some cases the I/O error encountered by CTTTPI is due to incompatible recording formats of different device types. To avoid the destruction of media originally created by another device, take care when handling the mounted volume, examining the I/O error messages on the console and in specifying the CTTTPI protection parameters.
In particular, the CTTTPI utility recognizes volumes that have never been accessed by the occurrence of an I/O error when it reads the label. If a 3490 device attempts to read a cartridge written by a 3490 device, an I/O error message is issued by the operating system that indicates format incompatibility, and the cartridge is treated by CTTTPI as a media to which data has never been written. In some cases the cartridges can be overwritten by a 3490 device. If your site has both media types and you want enhanced protection against the accidental mounting of cartridges created by a 3490 device and their re-initialization by a 3490 device, set PROTECT to PROMPT.
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