Appendix A. Performance data and statistics gathering 741
/SM590000Number of paths per host multipath device
The maximum supported number of paths per multipath device that is visible on the host is 
eight. Although the IBM Subsystem Device Driver Path Control Module (SDDPCM), 
related products, and most vendor multipathing software can support more paths, the 
Storwize V7000 expects a maximum of eight paths. In general, you see only an effect on 
performance from more paths than eight. Although the IBM Spectrum Virtualize can work 
with more than eight paths, this design is technically unsupported.
/SM590000Do not intermix dissimilar array types or sizes
Although the IBM Spectrum Virtualize supports an intermix of differing storage within 
storage pools, it is best to always use the same array model, Redundant Array of 
Independent Disks (RAID) mode. RAID size (RAID 5 6+P+S does not mix well with RAID 6 
14+2), and drive speeds. 
Rules and guidelines are no substitution for monitoring performance. Monitoring performance 
can provide a validation that design expectations are met, and identify opportunities for 
improvement.
IBM Spectrum Virtualize performance perspectives
IBM Spectrum Virtualize software was developed by the IBM Research Group. It is designed 
to run on commodity hardware (mass-produced Intel-based processors [CPUs] with 
mass-produced expansion cards) and to provide distributed cache and a scalable cluster 
architecture. One of the main goals of this design was to use refreshes in hardware. Currently, 
the Storwize V7000 cluster is scalable up to eight nodes (four control enclosures).
The performance is near linear when nodes are added into the cluster until performance 
eventually becomes limited by the attached components. Although virtualization provides 
significant flexibility in terms of the components that are used, it does not diminish the 
necessity of designing the system around the components so that it can deliver the level of 
performance that you want. 
The key item for planning is your SAN layout. Switch vendors have slightly different planning 
requirements, but the goal is that you always want to maximize the bandwidth that is available 
to the Storwize V7000 ports. The Storwize V7000 is one of the few devices that can drive 
ports to their limits on average; therefore, it is imperative that you put significant thought into 
planning the SAN layout.
Essentially, performance improvements are gained by selecting the most appropriate internal 
disk drive types, spreading the workload across a greater number of back-end resources 
when using external storage, and adding more caching. These capabilities are provided by 
the Storwize V7000 cluster. However, the performance of individual resources eventually 
becomes the limiting factor.