DB2 Storage Management and the Role of DFSMS

align
© 2013 Mullins Consulting, Inc.
DB2 and Storage Management
An Uneasy Partnership
Craig S. Mullins
Mullins Consulting, Inc.
http://www.craigsmullins.com

© 2013 Mullins Consulting, Inc. 2
Author
This presentation was prepared by:
Craig S. Mullins
President & Principal Consultant
15 Coventry Ct
Sugar Land, TX 77479
Tel: 281-494-6153
Fax: 281.491.0637
E-mail: craig@craigsmullins.com
This document is protected under the copyright laws of the United States and other countries as an unpublished work. Any use or
disclosure in whole or in part of this information without the express written permission of Mullins Consulting, Inc. is prohibited.
© 2013 Craig S. Mullins, Mullins Consulting, Inc. All rights reserved.

Agenda
DBA vs. Storage Administration
DB2 for z/OS and Storage
› Where does DB2 use storage?
› DB2 and DFSMS
› Newer DB2 Storage Features
Mainframe Disk Storage Options
What’s Still Missing?
Thoughts and Best Practices

How Many Shops Manage
DB2 and Storage Administration
DBA
Storage
Admin

DBA vs. Storage Administration
From a Storage Perspective
Database Administration
• Capacity planning for
database objects
• Database and data
management
• Database object interest
• Storage is sometimes an
afterthought
Storage Administration
• Capacity planning for
entire environment
• Disk and tape device
management
• Data set interest
• Storage is always top
of mind

6
But Something is Missing…
• There is a gap between Database Administration, Storage
Administration (DASD) and Capacity Planning.
• Storage management can be an afterthought for the DBA…
…but it shouldn’t be.
• According to Gartner, Inc. the cost of managing storage is
4-10 times the initial cost of storage acquisition.
• CAGR of disk storage was close to 60% between 2006 and 2011.
• Information is available to DBAs, but it is scattered and
difficult to show the full picture:
• DB2 RUNSTATS
• DB2 STOSPACE
• DB2 RTS
• Any historical view has to be managed manually.

Are You Prepared?
• Do all of my databases have sufficient allocation to satisfy
business requirements?
• Why is DB2 storage growing when our business is not?
• Am I wasting any storage?
• When will more storage be required?
• How much additional storage is needed?
• What needs to be done to align the additional storage with
the DBMS?
Can you answer all of the following questions
about your database storage requirements:

DB2 and Storage
› DB2 and DFSMS
› Modern Storage Architecture

• Tables do NOT consume storage (table spaces do)
– However, table definitions impact storage usage
– If an EDITPROC is used,
the maximum row length
is 10 bytes fewer
Tables Impact Page Size

Types of Table Spaces
Simple – max size 64 GB
› Contains one or more tables
› No new simple table spaces as of DB2 9
› Replace with universal table space partition‐by‐growth
Segmented – max size 64 GB
› Contains one or more tables
› Segments between 4 and 64 (multiples of 4)
Partitioned ‐ up to 4,096 partitions of up to 64 GB each
› Contains one table
› Usually used for larger tables
› Replace with universal table space partition‐by‐range
Universal ‐ up to 128 TB
› Combine partitioned and segmented characteristics
› Can contain both a base and a clone table
› Two types: Partition‐By‐Growth and Partition‐By‐Range
LOB – up to 16 TB
XML

DB2 Objects and Storage
• DB2 Storage Groups: list of disk
volumes
• Table Spaces: stored on disk as at
least one VSAM LDS data set
 Could be multiple: partitioned
• Indexes: stored on disk (in an index
space) as at least one VSAM LDS
data set
• System data sets
 Active Log: stored on disk
 Archive Logs: stored on disk or tape
 BSDS: stored on disk
• Image Copy Backups:
stored on disk or tape
• Other “stuff”
 DB2 library data sets
 Temporary data sets (used by utilities)

VSAM and Media Manager
• DB2 uses VSAM Media Manager for its I/O operations.
• For every I/O, VSAM Media Manager builds a channel program and sends a
request to the I/O supervisor.
DB2 uses VSAM (LDS) data sets “under the covers” to store data.

Multiple Data Sets per Object?
When does DB2 utilize multiple VSAM data sets for a table space or
index?
› When the object is partitioned. Each partition will reside in a
separate data set.
 And possibly more than one per partition.
› When a data set in a segmented (or simple) table space reaches its
maximum size of 2 GB, DB2 can automatically create a new data set.
› When the table space is cloned.
 Each clone has its own underlying data set(s).

Data Set Names
catname.DSNDBx.dbname.psname.y0001.z001
Integrated catalog name
or alias (up to eight characters).
C (for VSAM clusters) or
D (for VSAM data components).
database name
Page set name: either the table space name
or the index space name. Must be unique within
the database.
Instance qualifier for
the data set. y = I or J
(J is used when running online
REORG and CHECK utilities)1
Data set number: z = A, B, C, D, or E
For partitioned TS, the number is the
part number; A-E used for parts in excess
of 999.
For simple or segmented TS, start with
001 and increment by one as the TS
grows past max size of 2GB.
1 For cloned table spaces, there will be I0001 and I0002 – only one of which is “active”

Do You Monitor Your DB2 VSAM Data Sets?
TYPE DBNAME TS
NAME
IX
CRTR
IX
NAME
SPACE
NAME
SP
PRIQTY
SP
SECQTY
EX-
TENTS
DATA SET
NAME
TS DSNDB06 SYSDBASE SYSDBASE 60,480 60,480 4 DB2P.DSNDBD.SYSDBASE.I0001.A001
IX DSNDB06 SYSDBASE SYSIBM DSNACX01 DSNACX01 2,880 2,880 1 DB2P.DSNDBD. DSNACX01.I0001.A001
IX DSNDB06 SYSDBASE SYSIBM DSNATX01 DSNATX01 3,800 3,800 1 DB2P.DSNDBD. DSNATX01.I0001.A001
IX DSNDB06 SYSDBASE SYSIBM DSNDCX01 DSNDCX01 9,360 9,360 1 DB2P.DSNDBD. DSNDCX01.I0001.A001
IX DSNDB06 SYSDBASE SYSIBM DSNDCX02 DSNDCX02 5,760 5,760 1 DB2P.DSNDBD. DSNDCX02.I0001.A001
IX DSNDB06 SYSDBASE SYSIBM DSNDKX01 DSNDKX01 1,440 1,440 1 DB2P.DSNDBD. DSNDKX01.I0001.A001
. . . . . . . . . .
. . . . . . . . . .
. . . . . . . . . .

Where Can You Find DB2‐Related
Storage Information?
Online DB2 catalog Tool  http://www.z-dbs.com/zcat/zcat.php?version=11
• DB2 Catalog and Directory: stores metadata and control structures
• What about storage information?
– RTS = Real Time Stats
– When did you last run STOSPACE and RUNSTATS?

Storage Information in
The DB2 Catalog
SYSTABLESPACESTATS
› NACTIVE
› NPAGES
› EXTENTS
› SPACE
› TOTALROWS
› DATASIZE
› UNCOMPRESSEDDATASIZE
SYSTABLESPACE
› NACTIVEF
› AVGROWLEN
› SPACEF
SYSTABLEPART
› PQTY
› SQTY (or SECQTYI)
› STORTYPE
› STORNAME
› FREEPAGE
› PCTFREE
› SPACEF
› EXTENTS
SYSINDEXSPACESTATS
› NLEVELS
› NPAGES
› NLEAF
› NACTIVE
› SPACE
› EXTENTS
SYSINDEXES
› NACTIVEF
› AVGROWLEN
› SPACEF
SYSINDEXPART
› PQTY
› SQTY (or SECQTYI)
› STORTYPE
› STORNAME
› PSEUDO_DEL_ENTRIES
› FREEPAGE
› PCTFREE
› SPACEF
› EXTENTS
The DB2 Catalog tables are documented in an appendix of the DB2 for
z/OS SQL Reference - for V10 the manual number is SC19-2983

What About Compression?
CPU vs. I/O
› Consider compressing more table spaces than you currently do
› Hardware assisted compression is very efficient
› Compressed data can improve performance because more rows get
into the buffer pool
DSN1COMP
› Anything less than 25%, is probably not worth doing.
Compression dictionary is above the 2GB bar as of V8
› Allows for more table spaces that can be compressed

DB2 and Storage
› DB2 and DFSMS

DB2 Storage Options
Let DB2 manage the data sets using Storage Groups (STOGROUPs).
› Less work for DBAs… less control over data sets.
Let SMS manage some or all of the data sets.
› Available when you use DB2 storage groups or when you use data
sets you have defined yourself.
Define and manage your own data sets
using VSAM Access Method Services.
› More work for DBAs…
› More control over data sets…

Storage Groups
DB2 Storage Group
› DB2 uses STOGROUPs for
disk allocation of the table
and index spaces.
› It is basically just a list of
storage volumes
 Or ‘*’ for SMS
› A STOGROUP can be
assigned to:
 Databases
 Table spaces
 Indexes
SMS Storage Group
› An SMS Storage Group is a
pool of disk volumes upon
which SMS‐managed data
sets are placed.
› A data set is placed on an
appropriate volume within a
Storage Group depending
upon the Storage Class,
Volume, Storage Group
status, and available free
space.

Why Use DB2 Storage Groups?
When a table space is created, DB2 defines the necessary VSAM data sets
using VSAM Access Method Services.
When a table space is dropped, DB2 automatically deletes the associated
data sets.
When a data set in a segmented or simple table space reaches its maximum
size of 2 GB, DB2 can automatically create a new data set. The primary data
set allocation is obtained for each new data set.
DB2 can extend individual data sets as needed.
When you create or reorganize a table space that has associated data sets,
DB2 deletes and then redefines them, reclaiming fragmented space.
› If you run REORG with the REUSE option and SHRLEVEL NONE, REORG resets and
reuses DB2‐managed data sets without deleting and redefining them. If the size of
your table space is not changing, using the REUSE parameter could be more
efficient.
When you want to move data sets to a new volume, you can alter the
volumes list in your storage group. DB2 automatically relocates your data
sets during the utility operations that build or rebuild a data set.
› LOAD REPLACE, REORG, REBUILD, and RECOVER.

DFSMS
What is DFSMS?
› Data Facility Storage Management System
› Data management, backup and HSM software from IBM
mainframes.
› It combines separate backup, copy, HSM and device driver routines
into a single package.

DFSMS Components
• DFSMSdfp: Data Facility Product ‐ provides the logical and physical input
and output for z/OS storage, it keeps track of all data and programs
managed within z/OS, and it provides data access both for native z/OS
applications and other platforms.
• DFSMSdss is a priced optional feature. It is a DASD data and space
management tool for moving and copying data.
• DFSMShsm: Hierarchical Storage Manager ‐ a priced optional feature for
managing low‐activity and inactive data. It provides backup, recovery,
migration, and space management functions.
• DFSMSrmm: Removable Media Manager ‐ a priced optional feature for
managing removable media resources (e.g. IBM's Virtual Tape Server).
• DFSMStvs: Transactional VSAM Services – is another priced optional
feature that enables batch jobs and CICS online transactions to update
shared VSAM data sets concurrently.
DFSMS is actually multiple products; it is a suite of data
and storage management offerings.

DFSMS and DB2
Using DFSMS, a DB2 DBA can simplify the interaction of DB2 database
creation and storage specification. It can deliver:
› Simplified data allocation
› Improved allocation control
› Improved performance management
› Automated disk space management
› Improved data availability management
› Simplified data movement

Using SMS to Manage DB2 Data Sets
Managing DB2 Data Sets with DFSMS
• The DB2 administrator can use DFSMS to achieve all the
objectives for data set placement and design.
• DFSMS has the necessary flexibility to support everything the
DB2 administrator may want.
• There is no reason to not take advantage of DFSMS for DB2
data sets.
• To achieve a successful implementation, an agreement
between the storage administrator and the DB2
administrator is required so that they can together establish
an environment that satisfies both their objectives

DB2 and SMS
Defining a DB2 STOGROUP with VOLUMES (’*’) indicates
usage of SMS‐managed storage.
› With SMS, the system determines data set placement.
 Minimizes DBA work.
› Requires setup work in SMS using ACS
 For example, ACS can be used to differentiate between table spaces and
index data sets and place them on different devices.
› Consider using SMS to handle the majority of DB2 data set
placement
 Perhaps using non‐SMS techniques for high volume or special data sets

DB2 10, The Catalog and SMS
• SMS is a requirement for DB2 10 for z/OS
• The DB2 Catalog must be SMS‐managed as of V10
– The SMS environment that you use for DB2 catalog and
directory data sets must be established before you begin
migration to Version 10.
– DB2 10 requires a valid data class, management class,
and storage class
– No need to convert existing data sets
• They will be converted to SMS management when
the related table space is reorganized.

SMS Terms
Data Classes
› This is optional, although it is usually recommended that Data Classes be assigned. Even
though it is not saved for non SMS managed data sets, the allocation attributes in the Data
Class are used to allocate the data set.
Storage Classes
› Data sets use a Storage Class to qualify for SMS management. Here GUARANTEED SPACE is
specified, along with availability, performance, and accessibility characteristics.
Management Classes
› This is used for migration to level 1 and level 2 with or without backup, and indicates if there
should be no HSM management (backup or migration). It also includes expiration of data sets
and space release/compaction.
Storage Groups
› The Storage Group contains volumes that satisfy the service requirements of the data sets
allocated to them. They can handle more than one type of data. Separate Storage Groups
should be defined for production table spaces, active logs, other production data, and non‐
production data… a volume can only belong to one Storage Group
ACS (Automatic Class Selection)
› ACS routines assign data sets to SMS storage classes. For example, indexes can be assigned to
one SMS storage class and table spaces to a different SMS storage class.

DBA “Historical” Worries
Extreme data placement
› VCAT‐defined data sets for table spaces & indexes
Managing DB2 storage groups
› Carefully associating volumes to STOGROUPs
Extensive separation of data sets
› Examples
 careful placement to avoid contention
 always putting indexes on separate devices from data

User‐Defined VSAM?
• Less knowledge of VSAM and AMS is required
• DB2 manages external storage
(Data set deletion done by DROP TABLESPACE)
• Can ALTER primary and secondary allocation quantities
• Can switch to user-managed VSAM
• Can switch to other STOGROUPs
• More flexibility through the larger parameter set of AMS
• User-managed external storage
(including deletion of the data set)
• Can switch to STOGROUP-managed data sets
With user-defined VSAM files:
With STOGROUPs:

DB2 STOGROUPs
Many shops that have not migrated to SMS are using DB2
STOGROUPs for DB/TS/IX creation.
The STOGROUP Issue:
› Up thru DB2 V9: the list of volumes in the STOGROUP is
used “in that order” when allocating space
 VOLUMES(DV06, DV01, DV07)
› DB2 V10: the order “goes away” because there
are no more links in the DB2 Catalog

Reducing Extents
Modify PRIQTY / SECQTY and REORG
Storage Administrators have other methods of reducing extents
that (perhaps) can be quicker and/or easier:
› DFSMShsm MIGRATE and RECALL functions
› DFSMSdss COPY or DUMP and RESTORE functions
› DEFRAG with the CONSOLIDATE keyword
› Other products: e.g. Real Time Defrag

Data Set Placement?
• The new disk architectures, with concepts like log
structured files and with cache in the gigabyte
sizes, have a noticeable impact on database
physical design considerations.
• Conventional database design rules based on data
set placement are becoming less important and can
be ignored in most cases.

DB2 and Storage
› DB2 and DFSMS

Modern Storage Architecture
Disk… Tape… Array…
IBM DS8700 Disk
TS3500 Tape Library
TS3400 Tape Library
EMC Symmetrix Disk

A Disk is But a Disk?
Mainframe disk, or DASD, is equated to a 3380 or 3390.
In other words, physical hardware devices with a one‐to‐one
relationship between a disk drive and a volume. The logical
view is broken down as:
› Track size, or the number of bytes per track.
 47476 for 3380
 56664 for 3390
› Capacity, or the size of the device, in terms of number of tracks or
gigabytes.
› Device address, sometimes called device number, which is a thread onto
which I/O operations are serialized by the operating system
Today these physical devices are replaced by disk arrays.
› An array is the combination of two or more physical disk storage devices in
a single logical device or multiple logical devices.

From RAMAC (RVA) to ESS to DS
The RAMAC Virtual Array (RVA) came first for the mainframe and it was based on
virtual disks that emulated 3380s and 3390s.
› There is no fixed physical to logical mapping. The RVA dynamically maps functional volumes to
physical drives. This mapping structure is contained in a series of tables stored in the RVA
control unit.
› RVA was OEM'ed from Storage Technology Corp (now part of Oracle).
The ESS (Shark) followed when the STK OEM agreement expired.
› IBM technology; scalable from 420GB to 55.9 TB
› It offered improved performance (especially for prefetch and DSS)…
› But it lacked the virtual capability, at first.
The DS8000 employs virtualized disk. Adds additional functionality for:
› Storage Pool Striping ‐ a method of improving performance by allocating capacity to a logical
volume such that the capacity is spread over the set of ranks in the logical volume's extent
pool.
› Thin Provisioning – a method of configuring one or more logical volumes such that capacity
for data stored on the logical volume is not allocated until the data is written.
› Quick Initialization ‐ dynamically initializes logical volumes when they are created or
expanded allowing logical volumes to be configured and placed online more quickly
› Capacity scales linearly from 1.1 TB up to 192 TB (up to 320 TB with turbo models).

Disk Arrays: The Bottom Line
3390
Model
Cylinders Capacity
1 1,113 946 MB
3 3,339 2.83 GB
9 10,107 8.51 GB
27 32,760 27.84 GB
54 65,520 55.68 GB
• They use RAID and therefore are
virtual.
• Data is spread across multiple
physical disks in the array.
• Each I/O operation takes place
to, or from, several physical
disks.
• They emulate devices and map
logical disks to physical
locations.
Although the RVA, ESS, and DS8000 all work with logical disks
that map to physical locations, they are three different
architectures and are not the same type of hardware.
However, there are similarities:
Today’s disk arrays still emulate
the 3390 track architecture.

What is RAID?
• RAID = Redundant Array of Independent Disks
• The basic idea of RAID is this:
 Multiple disks configured together into an array.
 The array is perceived by the system to be a single disk device.
 Hot‐swappable drives improve availability
• A drive can be replaced while the array is up & running.
• There are many levels of RAID technology
 Each delivers different levels of fault‐tolerance and performance.
 Examples on next slide…

RAID Levels
Source: Advanced Computer & Network Corporation - http://www.acnc.com/04_00.html
(DS8000 and some ESS use RAID10)

DS8000: RAID10
› RAID10 is implemented as a striped array
whose segments are RAID 1 arrays.
› RAID 10 has the same fault tolerance as
RAID level 1.
› RAID 10 has the same overhead for fault‐
tolerance as mirroring alone.
› High I/O rates are achieved by striping
RAID 1 segments.
› Under certain circumstances, RAID
10 array can sustain multiple
simultaneous drive failures.
› Excellent solution for sites that
would have otherwise gone with
RAID 1 but need some additional
performance boost.
The IBM DS800 disk array is a RAID 10 implementation.

Popular Modern Disk Arrays
EMC Symmetrix
EMC V‐MAX
EMC DMX
Hewlett Packard XP24000/XP20000 Disk Array
Hitachi Data Systems Lightning
Hitachi Data Systems Universal Storage Platform
IBM System Storage ESS (Shark)
IBM System Storage DS6000
Sun StorageTek V2X4f

What About Disk Cache?
Buffer Pools and Disk cache are similar.
› Newer disk controllers have very large cache sizes and can retain
data for longer periods
Data is written from DB2 buffer pools to “disk” based on
your buffer pool and checkpoint settings.
› Deferred Write Threshold (DWQT) is reached when this pct. of
the buffer pool is allocated to unavailable pages (updated or in
use). DB2 schedules write I/Os to externalize data pages to disk.
› Vertical Deferred Write Threshold (VDWQT) is reached when this
pct. of the buffer pool is allocated to unavailable pages of a single
one data set.
› Checkpoint Frequency (CHKFREQ DSNZPARM) sets how often a
system checkpoint is taken (in minutes or log records); data is
“written” to disk at this point (among other things)

So What Happens When
DB2 Writes to Disk?
When DB2 writes to disk…
› DB2 destages updated data to the disk cache.
› DB2 treats this as a disk write, even though the write is to
cache.
› The data may or may not remain in the buffer pool depending
on why the data was destaged (DWQT, VDWQT, CHKFREQ).
› Data is also written to the NVS (Non Volatile Storage) part of
the disk controller that is battery backed.
 Even if the disk crashes, no data is lost.
› Based on disk thresholds, cache destages data back down to
disk.

Some z Storage Terminology
ESCON (Enterprise Systems Connection) is a data
connection created by IBM. It was used to connect
mainframe computers to peripheral devices such
as disk storage and tape drives.
FICON (Fibre Connectivity) is the IBM proprietary name for the
ANSI FC‐SB‐3 Single‐Byte Command Code Sets‐3 Mapping
Protocol for Fibre Channel (FC) protocol. It is a FC layer 4
protocol used to map both IBM’s antecedent (either ESCON or
parallel) channel‐to‐control‐unit cabling infrastructure and
protocol onto standard FC services and infrastructure.
› FICON has replaced ESCON in current deployments because of
FICON's technical superiority
 Higher performance and lower cost.

What About Solid State?
• The cost of solid-state drives (SSDs) is still high when
compared to spinning disks.
• Because SSDs have no moving parts, they perform better
than spinning disks (hard disk drives (HDDs)), and require less
energy to operate.
• In February 2009, IBM announced the DS8000 Turbo series
with solid-state drives.
• SSDs are plug-compatible in a DS8000 and are configured
using RAID in exactly the same fashion as HDDs.

zHPF
• Solid-state cause greater stress on the channel subsystem,
because SSDs enable higher levels of throughput.
• More improvements in the system as a whole enable solid-state
drives to further realize their full potential.
• IBM delivered High Performance FICON (zHPF) to the z/OS
environment to reduce system stress with SSDs.
• IBM recommends zHPF for an SSD environment.
• Even when the channel subsystem is not stressed, zHPF provides
lower response times when accessing SSDs.
• zHPF triples the maximum IO per second for random operations.
• When using z196 and R6.2, all DB2 I/Os are eligible for zHPF,
including format writes and list prefetch.
• These two types of I/O are the ones with the most to gain from zHPF.
More information can be found in “DB2 for z/OS and List Prefetch Optimizer” (redp4862)

MIDAW
MIDAW name stands for “modified IDAW.”
› An IDAW (indirect address word) is used to specify data
addresses for I/O operations in a virtual environment.
› This improvement is available as of the System z9™.
MIDAW is a hardware channel enhancement that
improves sequential access speed substantially for 4
KB page sizes.
MIDAW improves FICON performance, especially
when accessing DB2 databases, by reducing channel
utilization and increasing throughput for parallel
access streams.
More details: IBM RedPaper (redp4201)
How does the MIDAW Facility Improve the Performance of FICON Channels Using DB2 and other workloads?

DB2 Synchronous I/O Times
More studies can be found in “Ready to Access DB2 for z/OS Data on Solid State Drives” (redp4537)
“Short seeks” = an individual data set or an individual volume
being a hot spot.
“Long seeks” = when seeking between the extreme inner and
outer cylinders of a hard disk, but not very typical.

DB2 and Storage
› DB2 and DFSMS

Newer DB2 Storage Features
Extents
› Sliding Scale Extent Allocation
› Extent Consolidation
Variable CI Size
› Page size = CI size
CLONE Tables
As of V9, DB2 STOGROUP can define/alter SMS
constructs
› MGMTCLAS
› DATACLASS
› STORCLAS
DSNZPARMs

What About Extents?
For SMS‐managed data set you can have up to 123 extents on
each of 59 volumes.
› As of z/OS 1.7.
 So the limit is 7,257 extents for a data set;
 Instead of the 255 we were used to (for some time).
› To enable this, modify the DFSMS Data Class to set the Extent
Constraint Removal to YES.

OK, But Do Extents Still Matter?
Some folks think:
“With RAID/modern storage devices and new DB2 & z/OS
features, extents are no longer anything to worry about.”
This is not exactly true:
The latest extent management features only work with SMS‐
managed data sets, so if you are user‐managed old rules apply!
For SMS‐controlled data sets extents can still impact
performance.
› Each extent on a disk file has different control blocks
controlling access
› Elapsed time can increase if there is heavy insert activity
› Example:
 A program inserting 1m rows & using sliding extents with a very low
initial size doubled elapsed time compared to 1 extent
 May be caused by the allocation of each new dataset

Sliding Scale Extent Allocation
Enabled by setting MGEXTSZ to YES (DSNZPARM)
› Default is NO for V8
› Changed to YES automatically when you upgrade to DB2 9
Extent sizes allocated gradually increase
Maximum Extent size is based on DSSIZE
› Up to 16 GB the largest secondary extent
size is 127 Cylinders
› 32 GB & 64 GB the largest secondary
size is 559 Cylinders
As of V8, DB2 can allocate secondary extents automatically

Sliding Scale Extent Allocation
DB2 uses a sliding scale for secondary extent allocations of
table spaces and indexes when:
› You do not specify a value for the SECQTY option of a CREATE
TABLESPACE or CREATE INDEX statement
› You specify a value of ‐1 for the SECQTY option of an ALTER
TABLESPACE or ALTER INDEX statement.
Otherwise, DB2 uses the SECQTY value for secondary extent
allocations, if one is explicitly specified (and the SECQTY value
is larger than the value that is derived from the sliding scale
algorithm).
If the table space or index space has a SECQTY greater than 0,
the primary space allocation of each subsequent data set is
the larger of the SECQTY setting and the value that is derived
from a sliding scale algorithm.

The Sliding Scale Algorithm
If you do not provide a value for the secondary space allocation quantity,
DB2 calculates a secondary space allocation value equal to 10% of the
primary space allocation value and subject to the following conditions:
› The value cannot be less than 127 cylinders for data sets that range in initial size
from less than 1 GB to 16 GB, and cannot be less than 559 cylinders for 32 GB and
64 GB data sets.
› The value cannot be more than the value that is derived from the sliding scale
algorithm.
The calculation that DB2 uses for the secondary space allocation value is:
Actual secondary extent size = max ( 0.1 × PRIQTY, min ( ss_extent, MaxAlloc ) )
In this calculation, ss_extent represents the value that is derived from the
sliding scale algorithm, and MaxAlloc is either 127 or 559 cylinders,
depending on the maximum potential data set size. Secondary space
allocation quantities do not exceed DSSIZE or PIECESIZE clause values.

Extent Consolidation
Extent Consolidation
› Requires SMS‐managed STOGROUPs
› If new extent is adjacent to old, they will be merged together
› Some extents may end up being larger than the PRIQTY or SECQTY
specification(s)
› Introduced in z/OS 1.5

Variable CI Size
Beginning in Version 8, DB2 can define data sets with variable VSAM
control intervals.
› Prior to Version 8, DB2 defined all data sets with 4K CI size.
One of the biggest benefits of this change is an improvement in query
processing performance.
The VARY DS CONTROL INTERVAL parameter on installation panel
DSNTIP7 (DSVCI DSNZPARM) allows you to control whether DB2–
managed data sets have variable VSAM control intervals:
› YES ‐ indicates that a DB2–managed data set is created with a VSAM CI that corresponds to
the size of the buffer pool that is used for the table space. This is the default value.
› NO ‐ indicates that a DB2–managed data set is created with a fixed VSAM CI of 4 KB,
regardless of the size of the buffer pool that is used for the table space.

CLONE Tables
This is not the place for a comprehensive discussion of cloning but…
› Basically, cloning creates a table with the exact same attributes as a table that
already exists, except that it has no data.
› It is created using the ALTER TABLE SQL statement with the ADD CLONE parameter.
› The clone table is created in the same table space as the existing table.
 But in a different VSAM data set.
› After creating the clone table you can do whatever you want to do with it. LOAD it,
INSERT rows to it, etc.
› When the clone is ready to become the base table it is exchanged with the base
table. This is done using the EXCHANGE SQL statement.
› After running an EXCHANGE the clone becomes the
“real” table and the previously “real” table becomes
the clone ‐ ‐ and you can repeat the process.
Bottom Line
› You’ll need more storage to manage clones.

DB2 V9 STOGROUPs
If the data set that is associated with the storage group is not managed by
Storage Management Subsystem (SMS), VOLUMES must be specified.
› Asterisks are recognized only by SMS.
Having DB2 select the volume requires non‐SMS usage or assigning an SMS
Storage Class with guaranteed space.
› However, because guaranteed space reduces the benefits of SMS
allocation, it is not recommended.
If one or more of the DATACLAS, MGMTCLAS, or STORCLAS clauses are
specified, VOLUMES can be omitted. If the VOLUMES clause is omitted, the
volume selection is controlled by SMS.
Verifying the existence of volumes and classes: When processing the
VOLUMES, DATACLAS, MGMTCLAS, or STORCLAS clauses, DB2 does not
check the existence of the volumes or classes or determine the types of
devices that are identified or if SMS is active. Later, when the storage group
allocates data sets, the list of volumes is passed in the specified order to
Data Facilities (DFSMSdfp).

DSNZPARMs
SEQCACH BYPASS | SEQ
› Original meaning (for 3390) was whether DB2 I/O should
bypass the disk cache, but the meaning is different now
 BYPASS ‐ the disk will perform Sequential Detection
 SEQ ‐ creates an explicit Prefetch request
Recommendation: set to SEQ for improved performance
SEQPRES YES | NO
› Similar to SEQCACH, but for DB2 LOAD and REORG utilities
› If set to YES the Cache is more likely to retain pages for
subsequent update, particularly when processing NPIs
› Recommendation: set to YES

DSNZPARMs
MGEXTSZ YES | NO
› Whether or not DB2 will manage Sliding Extents?
› Note: the default changed to YES in DB2 9 (it was NO in DB2 V8)
TSQTY 0 and IXQTY 0
› Sets default object sizes if USING clause omitted
› Default values use 1 cylinder except for LOBs which use 10 cyls
DSVCI YES | NO
› Whether to use variable CI sizes
› Note this is turned on by default when you install V8
SVOLARC YES | NO
› YES means allocate a single volume for disk based archives
 Saves space if you use SMS guaranteed space option

DSNZPARMs
SMS Related DSNZPARMs
SMSDCFL
› Specifies a DFSMShsm data class for table spaces.
› If you assign a value to SMSDCFL, DB2 specifies that value
when it uses Access Method Services to define a data set for a
table space.
SMSDCIX
› Specifies a DFSMShsm data class for indexes.
› If you assign a value to SMSDCIX, DB2 specifies that value
when it uses Access Method Services to define a data set for
an index.

Wrapping It All Up

Examples of DB2 Storage “Things”
You Should Be Monitoring
1. Space display and monitoring of a DB2 system.
2. Space display and monitoring of Databases.
3. Space display and monitoring of the Table spaces (and Indexes).
4. Display and monitoring of the Storage Groups and the associated
volumes of a DB2 system. (Data, Workfile, Image Copies, Logs,
Archives, Sort/Work etc.)
5. VSAM display of all Table spaces and Indexes (Used, Allocated,
Primary and Secondary Quantity, Volumes) and monitoring of
Extents (physical and logical).
6. Display of the Linear Page Sets of Table spaces and Indexes, that
reach their maximum size (part. objects, DBSIZE) resp. the
maximum number of datasets (non-part. objects, PIECESIZE).
7. Intelligent HSM Migration of Image Copy Backup Data Sets, that are
not used for a local recovery (to CURRENT), as well as datasets older
than the last Full Image Copy (Dual and Remote Backups)
8. Delete of Image Copy Backup datasets of a DB2 system that are no
longer needed because of DROP, DROP/CREATE or MODIFY
TABLESPACE (‘orphaned‘, not listed in SYSIBM.SYSCOPY).

Best Practices
Keep up‐to‐date on DB2/storage functionality.
Perform regular and proactive monitoring.
Build alerts to inform you of problems,
shortages, and potential errors.
When possible, take automated action
in case of shortages, potential errors,
superfluous data sets, etc.

Contact Information
Craig S. Mullins
15 Coventry Court
Sugar Land, TX 77479
craig@craigsmullins.com
http://www.mullinsconsultinginc.com
http://www.craigsmullins.com/cm-book.htm
SoftwareOnZ
http://www.softwareonz.com
Offers zSPM, a comprehensive space
and SMS pool monitoring tool for
controlling, planning and automating
DB2 space management.

References
• Advanced Computer & Network Corporation, RAID.edu, http://www.acnc.com/04_00.html
• IBM Manual, DFSMS Introduction (SC26‐7397)
• IBM Manual, DFSMS Storage Administration Reference (for DFSMSdfp, DFSMSdss, DFSMShsm) (SC26‐7402)
• IBM Manual, DFSMS Implementing System‐Managed Storage (SC26‐7407)
• IBM RedBook, Storage Management with DB2 for OS/390 (SG24‐5462)
• IBM RedBook, Maintaining Your SMS Environment, (SG24‐5484
• IBM RedPaper, Disk Storage Access with DB2 for z/OS (redp4187))
• IBM RedPaper, DB2 for OS/390 Performance on IBM Enterprise Storage Server (redp0026)
• IBM RedPaper, DB2 for z/OS and List Prefetch Optimizer (redp4862)
• IBM RedPaper, How does the MIDAW Facility Improve the Performance of FICON Channels Using DB2 and
other workloads? (redp4201)
• IBM System z Storage Management Strategy
ftp://ftp.software.ibm.com/software/systemz/pdf/whitepaper/IBM_System_z_Storage_Management_Strategy_v1.1.pdf
• IBM DS8000 Storage Virtualization Overview
ftp://public.dhe.ibm.com/common/ssi/sa/wh/n/diw03020usen/DIW03020USEN.PDF
• Iczkovits, John, DB2 and Storage Management: a Guide to Surviving a Perfect Marriage, SHARE February 2008
• Mullins, Craig S., DB2 Developer’s Guide, 6th edition, Indianapolis, IN: SAMS Publishing: ISBN 0‐672‐32613‐4
• Smith, Ellin, DB2 UDB on z/OS Using EMC Symmetric Storage Systems Solution Guide, EMC Corporation, ISBN
9781604613407
• Thomas, Steve, Do Extent Numbers Really Matter Any More?, IDUG Europe 2008, Session A14
• Toigo, Jon William, The Holy Grail of Data Storage Management, Upper Saddle River, NJ: Prentice‐Hall: ISBN
0‐13‐013055‐9

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