Specifications

Chapter 2. Tapes (SCSI and awstape) 21
$ card2tape -a /tmp/myLinux.xyz /z/tape01 force translate ASCII to EBCDIC
The tape2tape command copies an emulated tape volume (awstape file in Linux) to another
emulated tape volume (another awstape file in Linux):
$ tape2tape /tmp/old.tape /z/new.tape
$ tape2tape -i -s /tmp/old.tape scan and summarize tape content
$ tape2tape -c /tmp/old.tape /mine/new.tape copy and compress
The -s flag (scan flag) prevents creation of an output file. The -i flag displays a summary of
the contents of the input tape. This command is normally used to compress or uncompress
an awstape volume, or to scan the content. A simple copy of an emulated tape volume
(without any additional processing) is easily done with the Linux cp command.
The tapePrint command lists the contents of an emulated tape volume. Data is displayed in
hex and character format. The characters are assumed to be EBCDIC unless the -a flag is
used.
$ tapePrint /tmp/my.awstape.file
$ tapePrint -a /tmp/my.awstape.file | more
Both the card2tape and tape2tape commands can produce compressed awstape files.
2.5 Practical advice
Most SCSI tape drives do not use vacuum columns to help manage tape start/stop times.
Instead they use slower mechanical methods to manage physical tape movement, which
means that starting and stopping the tape cannot be done in typical “tape gap” intervals.
The net effect is usually this:
򐂰 If the program (including the operating system elements) issues tape read (or write)
commands quickly enough, the tape drive will run the tape at full speed.
򐂰 If the program (including the operating system elements) does not issue reads (or writes)
quickly enough, the tape drive will stop after the current data block. The next read (or
write) may cause the tape drive to “backhitch” (that is, back up the tape for a distance) and
then start forward movement. This is done to ensure the tape is “up to speed” for the next
read or write operation.
This backhitch movement can greatly reduce the effective data speed of the drive. Not all
drives encounter this; other factors such as internal buffering may help avoid it. You can
typically hear the effects of a tape drive doing a backhitch for every data block.
If you encounter this situation, an alternative approach is to use the zPDT SCSI utilities, such
as scsi2tape, to copy the SCSI tape to an awstape emulated tape volume. The SCSI utilities
are fast and should not encounter any backhitching. Your application could then process the
emulated tape volume copy instead of the real SCSI tape volume. This may result in much
faster processing of your tape data.