Intel AS/400 RISC Server, 170 Servers, 7xx Servers manual 1000 2000 3000 4000 Ops/Sec

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

Time				RAID-5 Compared to RAID-6
			2780/574F (15 - 35 GB DASD): IOP, RAID-5
			571E/574F (15 - 35 GB DASD): IOPLess, RAID-5
Response
		0.2	571E/574F (15 - 35 GB DASD): IOPLess, RAID-6
	(sec)
		0.1
		0
System
		0	2000	4000	6000	8000	10000
				Workload Throughput

Time			RAID-5 Compared to RAID-6
			2780/574F (15 - 35 GB DASD): IOP, RAID-5
Response	(ms)		571E/574F (15 - 35 GB DASD): IOPLess, RAID-5
			571E/574F (15 - 35 GB DASD): IOPLess, RAID-6
		100
		50
DASD		0
		0	1000	2000	3000	4000
				Ops/Sec

IBM i 6.1 Performance Capabilities Reference - January/April/October 2008
© Copyright IBM Corp. 2008	Chapter 14 DASD Performance	199