Tony, Compression (as in ZIP) and compaction (as in IDRC tapes) are not the same process.
IDRC exploits the nature of IDRC compatible physical tape cartridges by writing everything using the cartridge's internal optimal physical block size. This is done by the cartridge drive's controller. So, ZIP based VTS compression, such as HET, is software; while IDRC compaction is hardware. There is no compression involved in IDRC, just hardware compaction. IDRC uses a process called "autoblocking" to transparently optimize how much data can fit on the cartridge's media by exploiting its optimal physical block size. Harry ________________________________ From: IBM Mainframe Discussion List <IBM-MAIN@LISTSERV.UA.EDU> on behalf of Tony Thigpen <t...@vse2pdf.com> Sent: Saturday, July 30, 2022 12:45 PM To: IBM-MAIN@LISTSERV.UA.EDU <IBM-MAIN@LISTSERV.UA.EDU> Subject: Re: AWS and IDRC/compression I am working with my VTA vendor to reduce storage usage on the appliance. Currently, they can compress after the unmount and uncompress before the mount. But, this takes time, especially when servicing the mount request if the tape is large. I was thinking that doing an IDRC implementation, which is stream based and performed during write/read, it might be faster even if it's not compresses as much as with their current method. But, if the AWS file is not compatible with IBM's implementation, then it's going to add a step to send them the file. The current compressed files can be uncompressed using standard linux tools. Tony Thigpen Jay Maynard wrote on 7/29/22 22:44: > I'm curious. What are you trying to accomplish with it? If it's just a > matter of faster transmission of entire tape images, AWS tapes compress > very well. > > On Fri, Jul 29, 2022 at 8:38 PM Tony Thigpen <t...@vse2pdf.com> wrote: > >> Yes. But, it sounds like nobody else will support it as a data >> interchange, so it may be unusable for us. >> >> I will go look at it. >> >> Tony Thigpen >> >> Jay Maynard wrote on 7/29/22 06:38: >>> Are you talking about the tape data being compressed inside the AWS >> image? >>> Hercules has a format that does this, upwardly compatible with AWS, >> called >>> HET (Hercules Emulated Tape), but I don't know of any other >> implementations >>> of it. Each block is compressed after being received from the program >>> writing the tape but before being written to the file and uncompressed >>> after being read but before being returned to the program reading the >> tape. >>> >>> On Fri, Jul 29, 2022 at 3:56 AM Tony Thigpen <t...@vse2pdf.com> wrote: >>> >>>> Does anyone know of any 'standard' for stream based (during file >>>> creation) compression of AWS tapes? >>>> >>>> Tony Thigpen >>>> >>>> ---------------------------------------------------------------------- >>>> For IBM-MAIN subscribe / signoff / archive access instructions, >>>> send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN >>>> >>> >>> >>> -- >>> Jay Maynard >>> >>> ---------------------------------------------------------------------- >>> For IBM-MAIN subscribe / signoff / archive access instructions, >>> send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN >> >> ---------------------------------------------------------------------- >> For IBM-MAIN subscribe / signoff / archive access instructions, >> send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN >> > > > -- > Jay Maynard > > ---------------------------------------------------------------------- > For IBM-MAIN subscribe / signoff / archive access instructions, > send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN
