Try // UNIT=(tape,2,AFF=ddname) And you can try increasing the drive numbers.
On Sat, Jan 11, 2025 at 1:59 PM Farley, Peter <[email protected]> wrote: > > 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 <[email protected]> On Behalf Of > Mike Schwab > Sent: Friday, January 10, 2025 7:44 PM > To: [email protected] > 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 > > <[email protected]> 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 [email protected] with the message: INFO IBM-MAIN -- Mike A Schwab, Springfield IL USA Where do Forest Rangers go to get away from it all? ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
