Chapter 4. Business continuance 37
the case of a database failure. The backup and recovery architecture has to
be designed according to the maximum acceptable unplanned downtime.
򐂰 Backup and recovery time included in SAP upgrade projects. The project
plan for an SAP upgrade always includes at least three backups of the SAP
database. The time needed to perform these backups will cut down the total
available time for the upgrade process.
4.1.1 IBM N series solution
IBM N series provides unique functionalities that address the previously
mentioned challenges.
IBM N series Snapshot can create an online or offline database backup in
seconds. The time needed to create a Snapshot copy is independent of the size
of the database, since Snapshot does not move any data blocks (Figure 4-1).
The use of Snapshot doesn't have any performance impact on the production
SAP system, since the IBM N series Snapshot implementation doesn't have to
copy data blocks when the data in the active file system is changed. Therefore,
creation of Snapshot copies can be scheduled without any concerns for affecting
the performance of dialog or batch activities. SAP and IBM N series customers
typically schedule several Snapshot online backups during the day-for instance,
every four hours.
Figure 4-1 Snapshot copies
© 2005 IBM Cor
p
oration
33
Snapshot
File/LUN: X
C’
WAFL always writes to a new,
performance-optimized location in RAID
Writes a single physical block for every
logical block-write
Some “copy-on-write” alternatives
require three operations (read old data,
save old data, overwrite with new).
A
B
C
Active Data
File/LUN: X
Disk blocks
Client sends new data
for block C
New
data
38 IBM System Storage N Series for SAP
Snapshot also provides key advantages for the restore and recovery operation.
The IBM N series SnapRestore functionality allows restoring the entire database
or parts of the database to the point in time of any available Snapshot copy. This
restore process is done in a few minutes, independent of the size of the
database. Because several Snapshot online backups have been created during
the day, the time needed for the following recovery process is also dramatically
reduced. Fewer logs need to be applied, because a restore can be done to an at
most four-hour-old Snapshot copy. The mean time to recover, which consists of
the time needed for restore and recovery, is therefore reduced to several
minutes, compared to several hours with conventional tape backups.
Snapshot backups are stored on the same disk system as the active online data.
Therefore, IBM recommends using Snapshot backups as a supplement, not a
replacement for backups to a second location, whether backup to disk or tape.
Though backups to a second location are still necessary, there is only a slight
probability that these backups will be needed for a restore and recovery. Most
restore and recovery actions will be handled by using SnapRestore. Restores
from a second location (disk or tape) are only necessary if the primary storage
system holding the Snapshot copies is damaged or there is the need to restore a
backup that is no longer available from a Snapshot copy-for instance, a
two-week-old backup. Restores from a second location can be considered as a
specific situation that will happen very rarely.
A backup and recovery solution using a IBM N series storage system will always
consist of two parts:
1. Backup and restore/recovery using Snapshot and SnapRestore
2. Backup and restore to/from a second location, which can be disk or tape (see
Figure 4-2 on page 39).

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