Investigating 571E/574F And 571F/575B Ioa, Bus And Hsl Limitations - IBM 170 Servers Manual

14.1.9 Investigating 571E/574F and 571F/575B IOA, Bus and HSL limitations.

With the new DASD controllers and IOPLess capabilities, IBM has created many new options
for our customers. Customers who needed more storage in their smaller configurations can now
grow. With the ability to add more storage into an HSL loop the capacity and performance have
the potential to grow. In the past a single HSL loop only allowed 6 5094 towers with 45 DASD
per tower, giving a loop a capacity of 270 DASD, with the new DASD controllers that capacity
has grown to 918 DASD. With the new configurations, you can see that 500 and even 600
DASD could make better use of the HSL loop's potential as opposed to the current limit of 270
DASD. Customer environments are unique and these options will allow our customers to look at
their space, performance, and capacity needs in new ways.
With the ability to attach so much more DASD to existing towers we want to try to characterize
where possible bottlenecks might exist. The first limits are the IOAs and we have attempted to
characterize the 571E/574F and 571F/575B in RAID and Mirroring environments. The next
limit will be the buses in a single tower. We are using a large file concurrent RSTLIB operations
from multiple virtual tape drives located on the DASD in the target HSL loop, to try to help
characterize the Bus and HSL limits. The tower is by itself in a single HSL loop, with all the
DASD configured into a single user ASP, and RAID5 activated on the IOAs.
As the scenarios progress 2 then 3 towers are added up to 6 in the HSL loop. All 6 have 3
571E/574F's controlling the 45 DASD in the 5094 towers and 3 571F/575B IOAs controlling
108 DASD in #5786 EXP24 Disk Drawer. Multiple Virtual tape drives were created in the user
ASP. The 3 other HSL loops contained the system ASP where the data is written to. We used
three HSL loops to prevent the destination ASP from being the bottleneck. The system was a
570 ML16 way with 256 GB of memory and originating ASP contained 916 DASD units on
571E/574F and 571F/575B IOAs. Restoring from the virtual tape would create runs of 100%
reads from the ASP on the single loop. The charts show the maximum throughput we were able
to achieve from this workload.
NOTE: This is a DASD only workload. No other IOAs such as communication IOAs were
present.
IBM i 6.1 Performance Capabilities Reference - January/April/October 2008
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Copyright IBM Corp. 2008 Chapter 14 DASD Performance 202