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In comparing Mirroring and RAID one of the concerns is capacity differences and the hardware
needed. We tried to create an environment where the capacity was the same in both
environments. To do this we built the same size database on “15 35GB DASD using RAID5”
and “14 70GB DASD using Mirroring spread across 2 IOAs”. The protection in the Mirrored
environment is better but it also has the cost of an extra IOA in this low number DASD
environment. For the 30 DASD and 60 DASD environments the number of IOAs needed is
equal.
14.1.7.3
14.1.7.4
IBM i 6.1 Performance Capabilities Reference - January/April/October 2008
© Copyright IBM Corp. 2008 Chapter 14 DASD Performance 200
RAID-5 compared to Mirroring
0
0.05
0.1
0.15
0.2
0.25
0 5000 10000 15000 20000 25000 30000 35000 40000
571E/574F (15 - 35 GB DASD): IOPLess, RAID-5
571E (14 - 70 GB DASD): IOPLess, 7 Mirrored Pairs 2 IOAs
571E (30 DASD): IOPLess, 15 Mirrored Pairs 2 IOAs
571E/574F (30 DASD): IOPLess, RAID-5 2 IOAs
571E (60 DASD): IOPLess, 30 Mirrored Pairs 4 IOAs
571E/574F (60 DASD): IOPLess, RAID-5 4 IOAs
Workload Throughput
System Response Time (sec)
RAID-5 compared to Mirroring
0
10
20
30
40
0 2000 4000 6000 8000 10000
571E/574F (15 - 35 GB DASD): IOPLess, RAID-5
571E (14 - 70 GB DASD): IOPLess, 7 Mirrored Pairs 2 IOAs
571E (30 DASD): IOPLess, 15 Mirrored Pairs 2 IOAs
571E/574F (30 DASD): IOPLess, RAID-5 2 IOAs
571E (60 DASD): IOPLess, 30 Mirrored Pairs 4 IOAs
571E/574F (60 DASD): IOPLess, RAID-5 4 IOAs
Ops/Sec
DASD Response Time (ms)