If you're just trying to prevent the B37-04 ABEND, let me recommend 'SPACE=(CYL,(274,273),RLSE),UNIT=(SYSDA,59)'. If the DSNTYPE=BASIC, there is a 4369-cylinder limit on z/OS data sets. 274 + (15 x 273) = 4369, These are the smallest primary and secondary allocations that will allow you to use 4369 cylinders on each volume. z/OS data sets cannot span more than 59 volumes, although I think the default is still 5 unless overridden with the DATACLAS.
As for determining the size of the data set, knowing how many bytes of data you're packing onto a track and then examining the number of cylinders used in ISPF option 3.4, can give you a good approximation of the amount of data currently stored. Od course, if you've ABENDed with an SB37-04, all of the data did not make it to disk. -----Original Message----- From: IBM Mainframe Discussion List <[email protected]> On Behalf Of Joseph Reichman Sent: Monday, June 29, 2026 8:28 PM To: [email protected] Subject: Re: Net bytes per track CAUTION: This email originated from outside of the Texas Comptroller's email system. DO NOT click links or open attachments unless you expect them from the sender and know the content is safe. Thanks I begging to have a better understanding I’m really trying figure out how many bytes in a dataset So by looking at dcbblksi its 32000 its a variable blocked. Record If the dataset got a b37 then all the space is used Up is there a programitclly way of determine the size of the dataset ? Thanks Get Outlook for iOS<https://urldefense.com/v3/__https://aka.ms/o0ukef__;!!JJZmGcLPLA!epaDRLe5xvuHQCHi2VN8_s_Qbkyd2Ty1wZmMTlncwEuxx9okMOzOi27oJDcBvleebVP3oaCwoT3fRs56Q0AL_BYXii3iNcRRIBH4PJiS11LX$ > ________________________________ From: IBM Mainframe Discussion List <[email protected]> on behalf of Michael Watkins <[email protected]> Sent: Monday, 29 June 2026 21:19:54 To: [email protected] <[email protected]> Subject: Re: Net bytes per track Yes, 56664 bytes per track on a 3390, but the maximum z/OS BLKSIZE is 32,760 bytes and only one block will fit on a track. To maximize the amount of data on a track, half-track blocking is typically used. There is a 668-byte inter-record gap on a native 3390 (platters on a spindle), which has been replicated on RAIDed FBA devices in modern DASD architecture. This means there is a maximum half-track BLKSIZE of 27998 bytes since 668+(2x27998)=56664. For a data set with 80-byte records, this means half-track blocking means a 27920-byte BLKSIZE since 349 x 80 = 27920 and there isn't room in 27998 for the 350th 80-byte record. Also keep in mind that z/OS will append 32 bytes onto each block when DSNTYPE=EXTENDED is specified, meaning less space for data records is available. -----Original Message----- From: IBM Mainframe Discussion List <[email protected]> On Behalf Of Joseph Reichman Sent: Monday, June 29, 2026 8:01 PM To: [email protected] Subject: Re: Net bytes per track CAUTION: This email originated from outside of the Texas Comptroller's email system. DO NOT click links or open attachments unless you expect them from the sender and know the content is safe. I keep on seeing from AI 56,664 bytes per tack for 3390 pack how is that determined Joe Reichman On Mon, Jun 29, 2026 at 8:58 PM Attila Fogarasi < [email protected]> wrote: > The net bytes (i.e. longest record you can write to that track) varies > by access method as there is overhead (control bytes). TRKCALC is > provided to compute the largest record which can fit on a track (using > EXCP), see > > https://urldefense.com/v3/__https://www.ibm.com/docs/en/zos/3.2.0?topi > c=instructions-performing-track-calculations-trkcalc-macro__;!!JJZmGcL > PLA!f8gIQp2WmnK5aJpNmmtG4m8kLdObQsseimGBKGffYscn-nyU3MS1l3Ja7JSZEZ7c6P > NPHimcV6MZ8a9Bu7MdeT39NLAkG2Cp0zXCYmzdsY2g$ > > Unless you are using EXCP the hardware track capacity is irrelevant, > the access method used will determine the actual bytes per track (and > varies by BLKSIZE). > > On Tue, Jun 30, 2026 at 10:35 AM Joseph Reichman < > [email protected]> wrote: > > > Would anyone know how to get the net bytes per track for a 3390 > > > > I have been using devtype ddname,buffer,devtab > > > > > > Where buffer is a 32 byte output field > > > > But it keeps on coming back with the overhead of 58,864 > > > > I think the net is 56,664 > > > > I would like to get that figure programmatically instead of hard > > coding > it > > > > Thanks > > > > -------------------------------------------------------------------- > > -- For IBM-MAIN subscribe / signoff / archive access instructions, > > send email to [email protected] with the message: INFO > > IBM-MAIN > > > > ---------------------------------------------------------------------- > For IBM-MAIN subscribe / signoff / archive access instructions, send > email to [email protected] with the message: INFO IBM-MAIN > ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
