Use the following settings on the external system:
- Set the ALUA mode to Enable because VSS block supports ALUA connection only. When the VSS block volumes are mapped, the ALUA mode is enabled by default. If you disable the ALUA mode, I/O performance might be degraded because I/O is issued on external paths that use VSS block ports with Active/Non-Optimized status.
- (VSP 5000 series) Use the default Normal Round-robin (recommended) for Load Balance Mode.
When the ALUA mode is enabled and Load Balance Mode is disabled, if the node restarts due to the VSS block software update and others, it might take about an hour to restore to the original I/O operation state.
- Set the number of VSS block nodes (physical servers) to no more than 8 and assign external paths equally to individual VSS block nodes.
For each LU in VSS block, the port status of one node is set to Active/Optimize, and the port status of other nodes is set to Active/Non-Optimize. On the other hand, the maximum number of external paths for the local storage system is 8 per LU. Therefore, if the number of VSS block nodes is 9 or more, the port status might be set to Non-Optimized for all external paths. As the result, when the number of VSS block nodes is 9 or more, I/O is issued on external paths that use VSS block ports with Active/Non-Optimized status, which might degrade I/O performance.
- (VSP 5000 series) When using an external volume of VSS block as an S-VOL of ShadowImage, set the I/O timeout value for the external path to 120 seconds (the default timeout value is 15 seconds). If a failure occurs on the VSS block node, it takes up to 120 seconds to replace the path.