The DS8### series allocates devices in multiples of 1113 Cylinders. Beyond 65520 cylinders, all EAV volumes are multiple of 1113 cylinders. The EAV portion is allocated in 21 cylinder amounts, with 53 groups of 21 cylinders per 1113 cylinders.
On Mon, Sep 16, 2013 at 6:57 AM, John Chase <[email protected]> wrote: > 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 > -- 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
