Ignore the bytes. In the EAV region, you get 53 groups of 21 cylinders for every 1113 cylinders.
On Tue, Sep 17, 2013 at 11:29 AM, Grantham, Charles <[email protected]>wrote: > Thanks for the response. I'm still a little confused by the 21 thing. By > my calculations 21*47,619,047 yields 999,999,987. > > The 8192 block size looks like a nice bit map for 65536; 65536/8 is 8192, > so the first area fits nice into a bitmap of 8K. Also when the theoretical > limit of 255tb (268,434,453 cyl) and divid it by 8192, the result is 7FFF + > a little, or a nice half word. The current limit of 262,668 cyl on a bit > map bases would fit nicely into 3+, 8192 blocks plus the original bit map > for the first 65520 tracks or four total; (262,668-65520)/(8*8192) = > 3.008+. All of this with the assumption that allocation is in 21 bit > chunks. > > OK, my brain hurts. > > The CA sizes makes a lot of sense to me. 315 (21*15) does yield some nice > number for CAs; (1,3,5,7,9,15). IMHO, a CA larger than 15 tracks doesn't > make a lot of sense and that really opens up the use of the 000 of the CCW > (CCCC000H) for EVA cylinder values. > > Hmmm. In a world of powers of two, this is a interesting venture. > > Chip Grantham > Sr. Software Engineer > Syncsort Incorporated > P: 201-882-8337 | C: TBD | F: 201-573-5176 > E: [email protected] > www.syncsort.com > > INTEGRATING BIG DATA… SMARTER > > -----Original Message----- > From: IBM Mainframe Discussion List [mailto:[email protected]] On > Behalf Of John Chase > Sent: Monday, September 16, 2013 7:58 AM > To: [email protected] > Subject: Re: Makes you go hmmmm, EVA MSU of 21 Cyls > > On Thu, 12 Sep 2013 09:13:39 -0500, Chip Grantham wrote: > > >I've finally taken the time to try to understand the numbers behind the > way EAVs were implemented. I found a great discussion in the redbook "z/OS > v1.12 Implimentation" SG24-7853-00 manual, chapter 20. Any time spend you > happen to spend here is worth it. (not unlike all redbooks). Thanks to > those that wrote it. > > > >I did happen into a segment that makes me go hmmm. 20.4.3 Multicylinder > unit section says the 21-cylinder value for the MCU is derived from being > the smallest unit that can map out the largest possible EAV and stay within > the index architecture (with a block size of 8192), as follows: > >* It is also a value that divides evenly into the 1 GB storage segments > >of an IBM DS8000, > >* These 1 GB segments are the allocation unit in the IBM DS8000 and are > equivalent to 1,113 cylinders. > > > >I'm sure the "index architecture" references the index vtoc architecture, > which has always been a curious archeture to me. Has this design ever been > made open? Just curious as to why it made 21 the magic number? > > > >I also ran into a math issue when I divided 21 into 1GB (or > 1,073,741,824/21 = 51,130,563.0476...). I suspect that's because the 1GB > storage segment is a number used in the DS8000 degisn, and its really close > to the 1GB value. Wondering if that's true or some other reason. > > IIRC, when discussing disk storage, "the industry" uses the decimal > meanings of KB, MB, GB, etc. Thus, a 1GB disk allocation would be > 1,000,000,000 bytes, which divided by 21 yields 47,619,047. > > -jc- > > ---------------------------------------------------------------------- > For IBM-MAIN subscribe / signoff / archive access instructions, send email > to [email protected] with the message: INFO IBM-MAIN > > > > ATTENTION: ----- > > The information contained in this message (including any files transmitted > with this message) may contain proprietary, trade secret or other > confidential and/or legally privileged information. Any pricing > information contained in this message or in any files transmitted with this > message is always confidential and cannot be shared with any third parties > without prior written approval from Syncsort. This message is intended to > be read only by the individual or entity to whom it is addressed or by > their designee. If the reader of this message is not the intended > recipient, you are on notice that any use, disclosure, copying or > distribution of this message, in any form, is strictly prohibited. If you > have received this message in error, please immediately notify the sender > and/or Syncsort and destroy all copies of this message in your possession, > custody or control. > > ---------------------------------------------------------------------- > 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
