64 Implementing the IBM Storwize V7000 with IBM Spectrum Virtualize V8.2.1
Apply the following general guidelines for back-end storage subsystem configuration 
planning:
/SM590000In the SAN, storage controllers that are used by the Storwize V7000 clustered system 
must be connected through SAN switches. Direct connection between the Storwize V7000 
and the storage controller is not supported. 
/SM590000Enhanced Stretched Cluster configurations have additional requirements and 
configuration guidelines. For more information about performance and preferred practices 
for the Storwize V7000, see IBM System Storage SAN Volume Controller and Storwize 
V7000 Best Practices and Performance Guidelines, SG24-7521.
If your back-end storage system does not support the Storwize V7000 round-robin algorithm, 
ensure that the number of MDisks per storage pool is a multiple of the number of storage 
ports that are available. This approach ensures sufficient bandwidth for the storage controller, 
and an even balance across storage controller ports. 
In general, configure disk subsystems as though Storwize V7000 was not used. However, 
there might be specific requirements or limitations as to the features usable in the specific 
back-end storage system when it is attached to Storwize V7000. Review the appropriate 
section of documentation to verify that your back-end storage is supported and to check for 
any special requirements at this website.
Observe the following general rules:
/SM590000Disk drives
Exercise caution with the use of large hard disk drives so that you do not have too few 
spindles to handle the load.
/SM590000Array sizes:
– Storwize V7000 does not queue more than 60 I/O operations per MDisk. Therefore, 
make sure that the MDisks presented to Storwize V7000 can handle about this many 
requests, which corresponds to about 8 HDDs. If your array can handle higher load, 
split it in several LUNs of equal size to better match back-end storage capabilities with 
the load that Storwize V7000 can generate. 
For more information about back-end storage LUN presentation to Storwize V7000, 
see IBM System Storage SAN Volume Controller and Storwize V7000 Best Practices 
and Performance Guidelines, SG24-7521.
– Since version 7.3, the system uses autoba lancing to restripe volume extents evenly 
across all MDisks in the storage pools.
MDisks within storage pools: Software versions 6.1 and later provide for better load 
distribution across paths within storage pools. 
In previous code levels, the path to MDisk assignment was made in a round-robin fashion 
across all MDisks that are configured to the clustered system. With that method, no 
attention is paid to how MDisks within storage pools are distributed across paths. 
Therefore, it was possible and even likely that certain paths were more heavily loaded than 
others. 
Starting with software version 6.1, the code contains logic that considers which MDisks are 
provided by which back-end storage systems. Therefore, the code more effectively 
distributes active paths based on the storage controller ports that are available. 
The Detect MDisk commands must be run following the creation or modification (addition 
of or removal of MDisk) of storage pools for paths to be redistributed.