When switches are used for distance connections, you can use host mode option (HMO) 51 to improve response times. The following figure shows a switch connection.
Using host mode option (HMO) 51 to improve response times
You can use HMO 51 (Round Trip Set Up Option) to improve response time of host I/O by improving response time between the storage systems when switches are used for distance connections (up to approximately 500 km with a round-trip response of 20 ms or less) and the open package is used.
| HMO | Function | Host mode | Description |
|---|---|---|---|
| 51 | Round Trip Set Up Option | Any | Use this HMO if you want to adjust the response time of the host I/O, for example when the distance between the primary and secondary storage systems in the TrueCopy or global-active device pair is long (approximately 100 km) and point-to-point topology is used. For further information, see the section below this table. |
As shown in the following table, Fab settings, topology settings, and available link speed depend on the settings of the packages and protocols used for the storage system connections, as well as whether host mode option (HMO) 51 is used. Some switch vendors require F port connectivity.
|
Package name |
Protocol |
HMO 51 setting |
Fabric setting |
Topology: Initiator and RCU Target |
Link speed that can be specified |
|---|---|---|---|---|---|
|
CHB(FC32G) |
32GbpsFC |
OFF |
ON |
Point-to-point |
|
|
ON |
ON |
Point-to-point |
|
||
| CHB(FC64G) |
64GbpsFC |
OFF |
ON |
Point-to-point |
|
|
ON |
ON |
Point-to-point |
|
HMO 51 details
- When the HMO 51 setting is changed to ON or OFF, a link-down and link-up occur on the target port, and an SSB log of link down is output on RCU (R-DKC).
- This HMO can work only when the microcode supporting this function is installed on both MCU (M-DKC) and RCU (R-DKC).
- This function is only applicable when the DW-F800-4HF32R PCB is used.
- When removing the DW-F800-4HF32R PCB, the operation must be performed after setting HMO 51 to OFF.
- If this option is used, Point to Point setting is necessary.
- If HMO 51 is set to ON while SOM 769 is ON, path creation might fail after automatic port switching.
- Make sure to set HMO 51 from OFF to ON or from ON to OFF after the pair is suspended or when the load is low.
- The RCU Target, which is connected with the MCU where this option is set to ON, cannot be used for Universal Replicator.
- Path attribute change (Initiator Port - RCU-Target Port, RCU-Target Port - Initiator Port) accompanied with Hyperswap is enabled after setting HMO 51 to ON. If HMO 51 is already set to ON on both paths, HMO 51 continues to be applied on the paths even after execution of Hyperswap.
- This function is available in the following configuration:
- Supported version: DW-F800-4HF32R: All versions
- Supported configuration: Point to Point setting with HMO 49 and HMO 50 set to ON while the path distance between MCU and RCU meets requirements of each program product. In the case of DW-F800-4HF32R, setting HMO 49 and HMO 50 is not necessary as it does not support the options.
Zoning a switch that is used to connect a remote path
When connecting a Fibre Channel port for the remote path to one FC-SAN (Fibre Channel Storage Area Network), consider the switch zoning.
Zoning offers the following advantages:
- The access range of Fibre Channel ports (Initiator port and RCU Target port) for the remote path can be separated from the access range of a different remote path or a different Fibre Channel port.
- If a failure occurs on a Fibre Channel port or a communication path, or when performing maintenance operations, the communication load on RSCN (Registered state change notification) can be limited to within the zone.
The following limitations apply when configuring zoning:
- If you configure zoning for purposes other than remote path operations, be careful not to affect the zoning configuration.
- Configure one zone for each remote path.
- If 16 or more Fibre Channel ports for the remote path are connected to one FC-SAN, make sure to configure zoning.
- If you change the zoning configuration while the remote storage system is in operation, consider the impact on remote I/O operations. If an incorrect zoning configuration is made, a problem such as not being able to communicate between remote paths might occur.