IBM Systems Magazine, Mainframe Edition - January/February 2012 - 38

Tips
only relate to the logical disk volume; they do not show the true picture of the physical layer. In our customer disk example, each DDM has a 300 GB raw disk capacity and emulation of a logical mod 27 device with 27.84 GB. This means that many other logical volumes are potentially striped across the same rank. Total and unrecoverable loss of a rank is no longer as potentially harmful as losing one physical volume. This may mean the loss of many logical volumes. Understanding virtualization of modern disks helps you realize that your data set doesn’t reside where you think it does. If you have a data set on one logical volume with one extent occupying 30,000 cylinders, based on our customer environment, your data is spread across many layers of 64 physical volumes. Your logical volume potentially co-resides with many other logical volumes on the same 64 physical volumes. Just because a data set is in one extent does not mean the data is contiguous. In our example, with the allocation spread across eight ranks and 64 volumes, the entire extent is noncontiguous. Where does your data set really reside from the physical layer? That’s a difficult question to answer. This can be challenging when doing performance analysis. VTOCs do not know about the modern physical layer. VTOCs have no cognition regarding ranks, arrays and DDMs. With rotate extents, when an extent reaches the end of space in a rank and is able to continue writing to the front of its next rank, the data now reside in two ranks. However, the VTOC does not know about the break and will still show the data residing in one extent. Let’s suppose I have a 25-cylinder data set in one extent with at least two ranks. Rank 1 only has the last full 15 cylinders of the 1,113 cylinders segment available. The remaining 10 cylinders of the allocation were able to reside at the beginning of rank 2, my 25 cylinders are still in one extent, but striped across two ranks. With a RAID 5 (7 + P) solution, my 25-cylinder data set in one extent is striped across 16 physical volumes.

Table 1
STRIPE OF 1,113 CYLINDERS
Rank 1 Rank 2 Rank 3 Rank 4 Rank 5 Rank 6 Rank 7 Rank 8 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Depending on the customer, mod 27 devices (actually mod 9 with 32,760 cylinders) will take the entire 32,760, which is 27.75 times a mod 3 device, or take up slightly less space to be an exact multiplier 27 times a mod 3. Rank numbers are for illustration purposes only. They are not actually called rank 1, 2, etc.

Look Ahead Data set placement should no longer be a full-time job. Modern sophisticated machines cannot be micromanaged. System Managed Storage (SMS) can be relied upon for placement, and the SMS separation profile, starting with z/OS* V1.11, can further be used to avoid hot

A Word About Tape
Modern tapes and cartridges can be manual, they can be automated tape libraries (ATLs) with robotics, or they can have some flavor of virtualization, such as the TS7720 tapeless tape or the TS7740. The TS7740 is front-ended by disk, but the data is eventually placed on physical tape using robotics. Deduplication solutions are also available. Other solutions deal with tape as well, such as Virtual Tape Facility for Mainframe. These solutions can be used in conjunction with each other. When MVS returns the location of a data set as a tape, allocations for the same physical tape cannot run in parallel as tape is serialized. DB2*, for example, could not use an archive log for parallel recoveries when MVS flags it as a tape data set, even though it may reside on a physical disk. —J.I.

spots, as necessary. There are very few cases—such as for the placement of the DB2* dual software copied active log and bootstrap data sets—where you must concern yourself with logical volumes on the same set of physical volumes. In today’s world of virtualization, where single-volume disk data sets reside on multiple physical disks and tape data sets may not reside on tape, I have to wonder: What will data look like in 25 years? I eagerly wait to see the amazing technological changes ahead of us.

John Iczkovits is a member of IBM’s DB2 Advanced Technical Skills team. His background includes a mix of MVS, Storage and DB2.

38 22

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IBM Systems Magazine, Mainframe Edition - January/February 2012

Table of Contents for the Digital Edition of IBM Systems Magazine, Mainframe Edition - January/February 2012

IBM Systems Magazine, Mainframe Edition - January/February 2012
Table of Contents
Editor’s Desk: Simplicity Itself
IBM Perspective: The Changing Data Center
Insider: Solve the DevOps Challenge With Orchestrated IT
Q&A: Guru Rao Explains How a Better World Begins With Smarter Computing
Case Study: A Comfortable Place: Furniture Brands rests easier with SecureAgent's backup and recovery solution
Cover Story: Smarter By Design: "That's the way to build capacity and hold costs flat," says IBM VP Doug Brown
Feature: Another Dimension: What sets the zEnterprise environment apart?
Tech Corner: How You Do What You Do When You're a z196 CPU
Tips & Techniques: Virtualization Reshapes How Data Is Stored
Solutions: CA Mainframe Application Turner - M4Workbench Eclipse - Virtual Machine Backup
Resources: Advertisers’ Index
Stop Run: Through Three Generations, One Family's Story Shows That While Technology Has Changed, IBM's Fundamental Mission Hasn't
Reference Point - Global events, Education, Resources of Mainframe
IBM Systems Magazine, Mainframe Edition - January/February 2012 - Intro
IBM Systems Magazine, Mainframe Edition - January/February 2012 - IBM Systems Magazine, Mainframe Edition - January/February 2012
IBM Systems Magazine, Mainframe Edition - January/February 2012 - Cover2
IBM Systems Magazine, Mainframe Edition - January/February 2012 - 1
IBM Systems Magazine, Mainframe Edition - January/February 2012 - Table of Contents
IBM Systems Magazine, Mainframe Edition - January/February 2012 - 3
IBM Systems Magazine, Mainframe Edition - January/February 2012 - 4
IBM Systems Magazine, Mainframe Edition - January/February 2012 - 5
IBM Systems Magazine, Mainframe Edition - January/February 2012 - Editor’s Desk: Simplicity Itself
IBM Systems Magazine, Mainframe Edition - January/February 2012 - 7
IBM Systems Magazine, Mainframe Edition - January/February 2012 - IBM Perspective: The Changing Data Center
IBM Systems Magazine, Mainframe Edition - January/February 2012 - 9
IBM Systems Magazine, Mainframe Edition - January/February 2012 - Insider: Solve the DevOps Challenge With Orchestrated IT
IBM Systems Magazine, Mainframe Edition - January/February 2012 - 11
IBM Systems Magazine, Mainframe Edition - January/February 2012 - 12
IBM Systems Magazine, Mainframe Edition - January/February 2012 - Q&A: Guru Rao Explains How a Better World Begins With Smarter Computing
IBM Systems Magazine, Mainframe Edition - January/February 2012 - 14
IBM Systems Magazine, Mainframe Edition - January/February 2012 - CT1
IBM Systems Magazine, Mainframe Edition - January/February 2012 - CT2
IBM Systems Magazine, Mainframe Edition - January/February 2012 - 15
IBM Systems Magazine, Mainframe Edition - January/February 2012 - Case Study: A Comfortable Place: Furniture Brands rests easier with SecureAgent's backup and recovery solution
IBM Systems Magazine, Mainframe Edition - January/February 2012 - 17
IBM Systems Magazine, Mainframe Edition - January/February 2012 - 18
IBM Systems Magazine, Mainframe Edition - January/February 2012 - 19
IBM Systems Magazine, Mainframe Edition - January/February 2012 - Cover Story: Smarter By Design: "That's the way to build capacity and hold costs flat," says IBM VP Doug Brown
IBM Systems Magazine, Mainframe Edition - January/February 2012 - 21
IBM Systems Magazine, Mainframe Edition - January/February 2012 - 22
IBM Systems Magazine, Mainframe Edition - January/February 2012 - 23
IBM Systems Magazine, Mainframe Edition - January/February 2012 - 24
IBM Systems Magazine, Mainframe Edition - January/February 2012 - 25
IBM Systems Magazine, Mainframe Edition - January/February 2012 - Feature: Another Dimension: What sets the zEnterprise environment apart?
IBM Systems Magazine, Mainframe Edition - January/February 2012 - 27
IBM Systems Magazine, Mainframe Edition - January/February 2012 - 28
IBM Systems Magazine, Mainframe Edition - January/February 2012 - 29
IBM Systems Magazine, Mainframe Edition - January/February 2012 - 30
IBM Systems Magazine, Mainframe Edition - January/February 2012 - Tech Corner: How You Do What You Do When You're a z196 CPU
IBM Systems Magazine, Mainframe Edition - January/February 2012 - 32
IBM Systems Magazine, Mainframe Edition - January/February 2012 - 33
IBM Systems Magazine, Mainframe Edition - January/February 2012 - 34
IBM Systems Magazine, Mainframe Edition - January/February 2012 - 35
IBM Systems Magazine, Mainframe Edition - January/February 2012 - Tips & Techniques: Virtualization Reshapes How Data Is Stored
IBM Systems Magazine, Mainframe Edition - January/February 2012 - 37
IBM Systems Magazine, Mainframe Edition - January/February 2012 - 38
IBM Systems Magazine, Mainframe Edition - January/February 2012 - Resources: Advertisers’ Index
IBM Systems Magazine, Mainframe Edition - January/February 2012 - Stop Run: Through Three Generations, One Family's Story Shows That While Technology Has Changed, IBM's Fundamental Mission Hasn't
IBM Systems Magazine, Mainframe Edition - January/February 2012 - Cover3
IBM Systems Magazine, Mainframe Edition - January/February 2012 - Cover4
IBM Systems Magazine, Mainframe Edition - January/February 2012 - Reference Point - Global events, Education, Resources of Mainframe
IBM Systems Magazine, Mainframe Edition - January/February 2012 - BG1
IBM Systems Magazine, Mainframe Edition - January/February 2012 - BG2
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