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What are the SolidFire FC cluster limits?

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Applies to

  • NetApp SolidFire All Flash Arrays
  • NetApp Element software

Answer

Below you will find an overview of what considerations should be made when designing, deploying, expanding, and supporting SolidFire Fibre Channel (FC) clusters:

I. Interplay between maximum numbers of FC initiators and volumes (also called Max IxL count) 

  • Maximum number of volume access groups (VAGs): 4 
    • Note: the 4 maximum access groups limitation is specific to FC; in iSCSI environments, a volume can belong to up to 64 volume access groups
  • Maximum number of volumes/LUNs within an access group: 2000 
  • Maximum number of FC Initiators (WWPN's) per access group: 64 
  • Maximum number of Initiators mapped to volumes (IxL count): 8000

When configuring the storage, it is possible to violate the maximum IxL count while staying within limits of maximum FC Initiators and volumes in a VAG.

To calculate the total IxL count, multiply (total FC initiators) * (total volumes) for each VAG, and then sum them up. If the sum is > 8000, you have violated the maximum IxL count. See SolidFire Fibre Channel Maximum I_T_L_Nexus count and IxL calculation for details.

II. Maximum number of simultaneous FC LUN Path Access (also called Maximum I_T_L Nexus count) 

The SolidFire FC node is equipped with sufficient resources to map 16,384 paths from LUNs back to initiators. It is quite easy to exceed this limit if care is not taken to carefully and intentionally zone Initiator access to specific FC Target ports. For details see Additional Information section.


III. Maximum number of Storage Nodes in an FC Cluster 

It is necessary to determine the total IOPS capability of the FC hardware installed in a cluster, and the total storage IOPS capability, to ensure that FC capabilities are always sufficient to serve the storage. 

For detailed information about this calculation, and guidance on the complexities and interplay between QoS settings and mixed-workload clusters, see SolidFire Fibre Channel Node Performance and Cluster Sizing Considerations.

Additional Information

Maximum number of simultaneous FC LUN Path Access:

Failure to take care of number of zone Initiator access to specific FC Target ports results in "Path Explosion" - where a single host might have far more paths to a LUN than intended and so unintentionally consumes many resources on the FC node.  It's possible to unintentionally configure 64 paths to a single LUN when only 4 paths were intended. 

The equivalent initiator-side limit is called the "Maximum Path Count" or the "Maximum Multipath Path Limit" and for most enterprise host installations this limit is 1024 or 2048 total paths in the whole system.  Being careful about the FC zoning configuration can also go a long way toward avoiding problems with host multipath drivers, as well as staying within the SolidFire FC Node maximum I_T_L Nexus count. 

For a detailed examination of the correct calculation of total I_T_L_Nexus count, or help in troubleshooting clusters with high path counts, see KB SolidFire Fibre Channel Maximum I_T_L_Nexus count and IxL calculation.

 

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