Thanks Mike, that does work to pre-mount the second volume of the first file, but unfortunately there isn’t much difference after that between using two units versus one. The Keep/Mount operations for the next needed volume don’t happen until EOF on the one being read, so there is no overlap between processing and Keep/Mount operations. WRT elapsed time, it looks like using one drive for the process is pretty much the same as using two.
In the days of actual tape drives, using two drives might have saved at least the rewind time for the next Keep/Mount (though I am not sure if even that would have happened – I never tested such a scenario in the days past when I actually had access to a “machine room”). Ah well, it was worth a try. I’ll stick with the one-drive solution, it gets the job done without any fuss. Peter From: IBM Mainframe Discussion List <IBM-MAIN@LISTSERV.UA.EDU> On Behalf Of Mike Schwab Sent: Friday, January 10, 2025 7:44 PM To: IBM-MAIN@LISTSERV.UA.EDU Subject: Re: Canonical way to limit a concatenated tape file DD to two tape drives? <URL to DD UNIT documentation><https://urldefense.com/v3/__https:/www.ibm.com/docs/en/zos/2.4.0?topic=up-syntax-1__;!!Ebr-cpPeAnfNniQ8HSAI-g_K5b7VKg!L7p1XrQ_mxQMddqz2--hMg0UGythO2kZGFh-OJ47bewWtMtPZBS9nVUhrnLkhc08CpEpzZ0vRj3Rn74uiiZyd8f1wlQgy_Fnk--IXV7p$> //ddname DD DISP=SHR,DSN=hlq.data.set.name1.llq, // UNIT=(tape,2) * device,count // DD DISP=SHR,DSN=hlq.data.set.name2.llq, // UNIT=AFF=ddname * repeat as needed On Fri, Jan 10, 2025 at 6:02 PM Farley, Peter <0000031df298a9da-dmarc-requ...@listserv.ua.edu> wrote: > > I have a business need to scan 15 different tape files (all the same record > format, some are multi-volume) to extract relevant information, and I first > tried to scan them all in one concatenated DD. I didn't specify anything but > DISP and DSN for each file in the concatenation, so I got 15 tape mounts to > 15 different tape drives. > > I would like to limit the tape drive usage so as not to unintentionally > interfere with production work that actually needs a tape drive. Using > UNIT=AFF=INPUTDD on the second and all other DD's in the concatenation limits > usage to ONE tape drive, the one allocated to the first file in the > concatenation. > > In order to reduce elapsed time for the scan job (each tape dismount/mount > operation takes an appreciable amount of time, usually at least a minute or > so), is there any way to use TWO drives in one concatenated DD instead of one > drive, so that as each file reaches EOF the process continues with the > already-mounted next file while the system loads the EOF drive with the next > file? If I knew in advance the device numbers of tape drives that are > actually available I could try to use UNIT=device1 and UNIT=device2 on > alternating DD's, adding ",,DEFER" to all but the first two DD's, but I don't > know what drives are available before I submit the job. > > If there is a way to use two drives without knowing the device numbers ahead > of time, what happens if one of the tape DD's is a file that has multiple > volumes? Does an already-mounted file from the next DD get dismounted to > load the next volume of the one being processed, or does it dismount the > first volume and wait for the next volume to be mounted on the same drive? > > These aren't "real" drives of course, they are all in a VTL, but the > principal is the same - don't occupy more devices than you really need. > > Peter > > This message and any attachments are intended only for the use of the > addressee and may contain information that is privileged and confidential. If > the reader of the message is not the intended recipient or an authorized > representative of the intended recipient, you are hereby notified that any > dissemination of this communication is strictly prohibited. If you have > received this communication in error, please notify us immediately by e-mail > and delete the message and any attachments from your system. -- This message and any attachments are intended only for the use of the addressee and may contain information that is privileged and confidential. If the reader of the message is not the intended recipient or an authorized representative of the intended recipient, you are hereby notified that any dissemination of this communication is strictly prohibited. If you have received this communication in error, please notify us immediately by e-mail and delete the message and any attachments from your system. ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN
