I used to use DISP=MOD solely for collecting SMF data - modding the
daily tape on the end of the monthly SMF tapes. It was mostly
reliable, but when it failed, which it did a few times over the years,
you lost a good chunk of your SMF data for the month.
One of the problems with MOD for SMF data is that SMF data is RECFM=VBS,
spanned. This means that almost every block (except the first and last
written) will be spanned, containng the end of one logical record or the
beginning of the next, or both. If the last write to the tape was
terminated prematurely or got an I/O error on WRITE, or an I/O error
reading back, then when reading the tape you can get S002 abends because
spanning errors.
Back when I worked for a end-user site, I once spent two days writing
custom programs to recover from such an error.
When I came to Innovation, my first assignment was FATAR, our tape
copy/recovery utility, and one of the first functions I added was
identification and recovery from VBS spanning errors.
The unfortunate part was that the errors were unnecessary. SMF data can
be changed to RECFM=VB,LRECL=32756,BLKSIZE=32760 when copying it,
avoiding any spanning problems.
--
Bruce Black
Senior Software Developer
Innovation Data Processing
----------------------------------------------------------------------
For IBM-MAIN subscribe / signoff / archive access instructions,
send email to [EMAIL PROTECTED] with the message: GET IBM-MAIN INFO
Search the archives at http://bama.ua.edu/archives/ibm-main.html
