IBM DS8000 manual Performance and sizing considerations for open systems

switch has two ports to connect to the next switch pair with 16 DDMs when vertically growing within a DS8000. As outlined before, this dual two logical loop approach allows for multiple concurrent I/O operations to individual DDMs or sets of DDMs and minimizes arbitration through the DDM/switch port mini loop communication.

12.3.5 Vertical growth and scalability

Figure 12-9shows a simplified view of the basic DS8000 structure and how it accounts for scalability.

Server 0	L1,2		I/O enclosure	I/O enclosure		L1,2	Server 1
Memory	Memory	Processor
					Processor	Memory	Memory
L3	L1,2	Processor	RIO-2 Interconnect			L1,2	L3
	Memory				Processor
Memory						Memory	L3
							Memorye ory
POWER5 2-way SMP	RIO-G Module		I/O enclosure	I/O enclosure	RIO-G Module
							POWER5 2-way SMP
			Dual two-way processor complex
			Fibre Channel switched disk subsystems are not shown
Server 0	L1,2					L1,2	Server 1
Memory	Memory	Processor
					Processor	Memory	Memory
L3	L1,2	Processor	RIO-2 Interconnect		Processor	L1,2	L3L3
Memory	Memory					Memory
							Memorye ory
RIO-G Module			Dual four-way processor complex			RIO-G Module
	L1,2	Processor				L1,2
Memory	Memory				Processor	Memory	Memory
L3	L1,2	Processor	RIO-2 Interconnect			L1,2	L3
	Memory				Processor
Memory						Memory	L3
							Memorye ory
RIO-G Module						RIO-G Module
	POWER5 4-way SMP				POWER5 4-way SMP

Figure 12-9 DS8100 to DS8300 - scale performance linearly - view without disk subsystems

Although Figure 12-9does not display the back-end part, it can be derived from the number of I/O enclosures, which suggests that the disk subsystem also doubles, as does everything else, when switching from a DS8100 to an DS8300. Doubling the number of processors and I/O enclosures accounts also for doubling the performance or even more.

Again note here that a virtualization layer on top of this physical layout contributes to additional performance potential.

12.4 Performance and sizing considerations for open systems

To determine the most optimal DS8000 layout, the I/O performance requirements of the different servers and applications should be defined up front since they will play a large part in dictating both the physical and logical configuration of the disk subsystem. Prior to designing the disk subsystem, the disk space requirements of the application should be well understood.

264DS8000 Series: Concepts and Architecture