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00561 - Journaling to separate User-ASP
PERFORM Short Reference CPI1466 during BackupThis documentation is copyright by SAP AG.
Journaling to separate User-ASP
Hi all!Backup and recovery V4R5 says:
http://publib.boulder.ibm.com/cgi-bin/bookmgr/BOOKS/QB3ALE04/6.2.2.6
Nothing new, I would say.
The Performance Capabilities Reference
http://publib.boulder.ibm.com/cgi-bin/bookmgr/BOOKS/AS4PPCP3/CCONTENTS
pointing to a PDF:
http://publib.boulder.ibm.com/pubs/pdfs/as400/V4R5PDF/AS4PPCP3.PDF
has more to say:
From Page 65:
---QUOTE---
The impact to performance from adding journaling can be reduced by locating
the journal receiver on a separate user ASP. Doing this will generally
reduce
the seek time required to access the disk arms for journal I/O which will in
turn help reduce the impact to end user response time. It will also lessen
the
impact to the disk arms located on the system ASP.
When using a separate user ASP for journal receivers,
it is important to consider the number of disk actuators available in the
ASP.
Customer environments with heavily used journal receivers located in a user
ASP
that consists of a single disk actuator may actually reach a limit to
performance
because of the high usage of this single actuator. In this case, it would be
better to have multiple disk actuators available in the user ASP so that
DB2/400 journaling support can interleave journal entries over the multiple
actuators, thus reducing contention for any one single disk arm. Doing this
may result in an improvement in response time and in overall system
throughput.
However, it is important to note that although adding an actuator may
provide
a significant improvement in performance, each additional actuator added
beyond
this will improve performance to a lesser degree. Once the utilization of
the
actuators is low, adding more actuators will not improve performance.
Having two or more journal receivers located on the same user ASP and having
them in use at the same time may not take full advantage of the performance
gains seen by isolating a single journal receiver on the User ASP since the
seek distance on the actuator increases as the journal entries are written
to the two receivers.
---UNQUOTE---
As this is from the V4R5 book, the recommendation has not changed
over time.
On all production machines, we have the JrnRcvs in ASP2 with mirrored
disks, one machine with 2 pairs for one journal, the other one with
3 pairs for two journals of two instances.
HTH
Rudi
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SAP R/3 BASIS & /\ Fax: +43 - 0732 / 7070 - 54 1720
AS/400 Professional System Administrator (IBM Certified Specialist)
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