On 05/02/2010 08:26 PM, Scott Barry wrote: > On Sun, 2 May 2010 08:46:49 -0400, Lizette Koehler <[email protected]> > wrote: > >> I have a project to review all the virtual tapes in the VTS and see which >> tape datasets could go on dasd. >> >> I am using CA1 to get the LRECL, BLKSIZE and BLKCNT to determine how many >> bytes are on the tape. Then dividing that by the number of bytes per track >> to get a rough estimate. >> >> Is there a better way of doing this? I have over 100,000 tapes to review >> and I am trying to make sure I have a good process. >> >> Or is there a different formula I should be using other than >> bytes = lrecl * blksize * blkcnt (and if blkcnt = 0 I >> set blkcnt = 1) >> >> Lizette > > > I'm curious how you might be expecting to factor in IDRC compression with > the data stored on the tape? I believe that the BLKCNT represents what is > being stored, not what got sent down the channel. > > Also, there has been reported conditions where a BLKSIZE is not reported to > the tape mgmt system on CLOSE, so the BLKSIZE shows up as zero -- some years > ago, ADRDSSU and CA-VIEW each exhibited this behavior - since then it's been > fixed. For my tape inventory analysis exercises, I used a default of 32760, > when not reported. > > Scott Barry > SBBWorks, Inc. > On tape drives with IDRC or other compression, MVS is only aware of logical blocks sent across the channel, not the physical representation on the tape (except very indirectly by indicators of % of media used). My understanding is that with compression, the compressed logical blocks are assembled by the tape controller into "super blocks" that are written on the physical tape, but that structure is not communicated back to MVS because those are issues that are completely handled at the tape controller level.
For many years (while reporting a blocksize of 0 to the Tape Management System), ADRDSSU was somehow writing a logical block size of 64 KiB on 3480/3490. Unless your old ADRDSSU tapes are over a decade old, 32 KiB is probably too low a value for those. I remember vaguely when the DSS change to 64 KiB occurred, because our older stand-alone-IPL DSS tape wouldn't work on the newer backups and you had to be sure to have a newer version to be covered for DR. -- Joel C. Ewing, Fort Smith, AR [email protected] ---------------------------------------------------------------------- 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
