72 Storage Management with DB2 for OS/390
means that a large number of image copy data sets are required and need to be
managed.
Data Organization
Image Copy data sets are physicalsequential data sets. Record size is 4096 (for
any size of page) and the block sizeis typically 28672 bytes. Sample statements
to executean image copy are shown in Figure 137 on page 198 inA ppendixB,
section B.3, “Image Copies” on page 194.
Performance
Most image copies haveno special performance requirements, but there are
cases when the time to take an image copy becomes critical.
Availability
Image copies ensure user and system data integrity. Their availability is critical
for DB2 system and application availability.DB2 can optionally generate up to
four imagecopies of a table space or of a data set (for a multipledata set table
space). Twoof these copies are intended for a disasterrecovery at a remote site.
Migration
Image copies can be created on tape, or on disk. Image copies are eligible for
migration.Some inst allationscreate image copies on a pool of disks and migrate
asynchronously later inorder to avoid delays due to contention for tapeunits. If
multiple image copies are created, then a technique such as that described for
archive logsm aybe us ed to ensure deviceseparation for the different copies.
Backup
Image copies are backupsof system and user data. Multiple copies can be
generated.A previous image copy can act as backup for the most recent one, but
then more log needs to be applied during the recovery process. Additional
backupsi mproveimage copy availability and more frequent image copies reduce
recovery time.
7.5.1 Storage Class
This example assumesdifferent availability and performance requirements for
image copies.Because of this, two Storage Classes have been definedfor image
copies.
• SCDBIC
• SCDBICH
7.5.2 Management Class
This examplesas sumes differentretention cycles for image copies. This is
reflected in fourM anagement Classes:
• MCDBICD - Daily image copies
• MCDBICW - Weekly image copies
• MCDBICM - Monthly image copies
• MCDBLV2 - Secondary image copies