CNS usage considerations

Server and Cluster Administration Guide for Hitachi NAS Platform

Part Number

The following recommendations are intended to simplify configuration and maintenance for CNS and for transfers of primary access for the file system:

  • A single name space is supported per server or cluster.
  • If there is only one CNS link to the file system, and no SMB shares/NFS exports on the file system, only a single link has to be moved during a transfer of primary access.
  • CNS does not support hard links or move operations across the individual file systems. These operations are fully supported, but only within a single physical file system; that is, the part of the CNS tree under a file system link.
  • Relocating file systems under the CNS may interrupt SMB access to the file system being relocated. To minimize interruption, relocate file systems when they are idle. For more information, refer to the Replication and Disaster Recovery Administration Guide.
  • When using CNS and EVS together:
    • Only one EVS per cluster node is required for all data inside the cluster name space. Having additional EVSs causes unnecessary administrative overhead, and may lead to confusion. Use multiple EVSs on the same cluster node only when you have data that should reside outside the cluster name space.
    • Balance loads by moving file systems, instead of migrating EVS. If you migrate an EVS containing a read cache, the files in the read cache become invalidated and, assuming they are still cacheable, they would have to be cached again after the next read request.

      If an EVS containing a read cache is migrated to another cluster node that already has a read cache, the files in the migrated read cache are invalidated, and only the read cache that was not migrated will be used. If the EVS is migrated back to its original cluster node, the read cache will be used again, assuming another read cache has not been created on that cluster node in the interim.

  • When using CNS, the recommended configuration is to have a single SMB share or NFS export at the root of the name space. If that configuration does not suit your needs, the next best configuration is to have SMB shares/NFS exports pointing to individual directories in the name space. You should not configure SMB shares or NFS exports pointing to a path of the real file system unless absolutely necessary.
    Note: A VSP N series or VSP Gx00 or VSP Fx00 with NAS modules is a two node cluster in a single chassis. The CNS support on the default two node cluster is automatic. Both nodes have access to the shared storage, and the CNS traffic is sent to the other node.