Before configuring a system using Fibre Channel, there are restrictions that you need to consider. For details about Fibre Channel, see the Provisioning Guide for your system.
- When you use 32-Gbps Fibre Channel as a remote path, if you specify Auto for Port Speed, specify 10 seconds or more for Blocked Path Monitoring. To specify the port speed, use the raidcom modify port command. To specify the time length of blocked path monitoring, use the raidcom modify remote_replica_opt command.
- If you want to specify 9 seconds or less, do not set Auto for Port Speed. If the time specified for Blocked Path Monitoring is not long enough, the network speed might be slowed down or the period for speed negotiation might be exceeded. As a result, paths might be blocked.
- When multiple remote paths share a port, set the same value of path blocked watch SIM time (time for watching SIMs reported when paths are blocked) for all remote paths.
- If you want to change the port topology setting (Fabric, FC-AL, Point-to-Point), delete the remote path first. If you change the port topology setting while a remote path is being used, the topology settings of the host and the storage system do not match, possibly resulting in remote path blockage. Use the raidcom modify port command to change the port topology.
- If you want to use 64-Gbps Fibre Channel as a remote path, read the caution on setting the data transfer speed to the Fibre Channel port of your storage system in the Provisioning Guide beforehand.
The following table shows the blocked path monitoring time you can set when you use 64-Gbps Fibre Channel as a remote path and set one of the following port speed options. Use the same table as reference for the blocked path monitoring time for remote paths from remote devices to the VSP One B20 series storage system. If the VSP One B20 series storage system uses 64-Gbps Fibre Channel, set the value in the table regardless of whether the type of Fibre Channel used by the remote system is 64 Gbps, 32 Gbps, or 16 Gbps.
Port speed setting for 64-Gbps Fibre Channel
Blocked path monitoring time
Impact on remote copy function if a temporary path-wide failure occurs
Fixed to 64 Gbps, 32 Gbps, or 16 Gbps
Less than 35 seconds (not recommended)
The remote copy pair might be suspended by failure.
35 seconds or more (recommended)
The path is restored within the blocked path monitoring time and the remote copy pair retains PAIR status.
Auto
- (not recommended)
The remote copy pair might be suspended by failure.
If the blocked path monitoring time is less than 35 seconds, pairs might be suspended by failure due to a temporary all-path failure. If you do not want to suspend pairs due to a temporary all-path failure, set 35 seconds or more for the blocked path monitoring time.
When you use 64-Gbps Fibre Channel as a remote path, fix the transfer speed of all fibre switches, extenders, and remote devices to 64 Gbps. If the transfer speed of any of the fibre switches, extenders, and remote devices cannot be set to 64 Gbps, set the port speed of the VSP One B20 series storage system to "fixed to 32G" or "fixed to 16G".
When you use 64-Gbps Fibre Channel as a remote path, the recovery time from an intermittent failure is longer than 32 Gbps. If the response performance at the intermittent failure is important, do not use 64-Gbps Fibre Channel.
- If you want to reduce the impact of response time to the host if a
failure occurs in some part of the remote path, set system option mode 784 to ON. By
doing so, the time before switching to a redundant path is reduced if the remote
path fails, allowing you to continue I/O in an environment where the host timeout
time is short. However, the following disadvantages might occur when system option
mode 784 is set to ON:
- The host might time out if the new switched path also fails.
- If the MP unit of the controller to which the remote path belongs is overloaded, switching of paths might be delayed, causing the host to time out.
- If an I/O retry occurs for the remote path due to a reason other than RIO MHI time, such as reporting of a check condition from the RCU to the MCU, the retry is performed on the same path. In a situation where I/O response delay for the remote path occurs regularly due to a path failure or a line failure on the path in question, if the delay does not exceed 5 seconds, retries continue to be performed on the same path. As a result, the host might time out.
- Even if system option mode 784 is set to ON, if the host timeout time is 10 seconds or less, the host might time out.
- The RIO MIH time is fixed to 5 seconds and it is not the user-defined value (default is 15 seconds and you can set a value between 10 and 100 seconds). The RIO MIH time displayed by CCI is a user-defined value.