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14.1.7 Comparing 571E/574F and 571F/575B RAID5 and RAID6 and Mirroring
System i protection information can be found at http://www.redbooks.ibm.com/ in the current
System i Handbook or the Info Center http://publib.boulder.ibm.com/iseries/ . When comparing
RAID5, RAID6 and Mirroring we are interested in looking at the strength of failure protection vs
storage capacity vs the performance impacts to the system workloads.
A model 570 4 way system with 48 GB of mainstore memory was used for the following. First
comparing characteristics of RAID5 and RAID6; a customer can use Operations Navigator to
better control the number of DASD in a RAID set but for this testing we signed on at DST and
used default available to turn on our protection schemes. When turning on RAID5 the system
configured two RAID sets under our IOA, one with 9 DASD and one with 6 DASD with a total
disk capacity of 457 GB. For RAID6 the system created one RAID set with 15 DASD and a
capacity of 456 GB. This would generally be true for most customer configurations.
As you look at our run information you will notice that the performance boundaries of RAID6 on
the 571E/574F is about the same as the performance boundaries of our 2780/574F configured
using RAID5, so better protection could be achieved at current performance levels.
Another point of interest is that as long as a system is not pushing the boundaries, performance is
similar in both the RAID5 and RAID6 environments. RAID6 is overwhelmed quicker than
RAID5, so if RAID6 is desired for protection and the system workloads are approaching the
boundaries, DASD and IOAs may need to be added to the system to achieve the desired
performance levels. NOTE: If customers need better protection greater than RAID5 it might be
worth considering the IOA level mirroring information on the following page.
14.1.7.1
14.1.7.2
IBM i 6.1 Performance Capabilities Reference - January/April/October 2008
© Copyright IBM Corp. 2008 Chapter 14 DASD Performance 199
RAID-5 Compared to RAID-6
0
50
100
0 1000 2000 3000 4000
2780/574F (15 - 35 GB DASD): IOP, RAID-5
571E/574F (15 - 35 GB DASD): IOPLess, RAID-5
571E/574F (15 - 35 GB DASD): IOPLess, RAID-6
Ops/Sec
DASD Response Time
(ms)
RAID-5 Compared to RAID-6
0
0.1
0.2
0 2000 4000 6000 8000 10000
2780/574F (15 - 35 GB DASD): IOP, RAID-5
571E/574F (15 - 35 GB DASD): IOPLess, RAID-5
571E/574F (15 - 35 GB DASD): IOPLess, RAID-6
Workload Throu
g
h
p
ut
System Response Time
(
sec
)