LUN Writeback Without Mirroring

Procedure

Go to the Modify LUN dialog box.
1. Log in to the ISM. In the navigation tree, choose All Devices > SN_XX > Storage Resources > LUNs, where SN_XX indicates a storage system.
2. In the function pane, select the desired LUN.
3. Click Modify.
  The Modify LUN dialog box is displayed.
Modify Write Policy of the LUN to Write Through. Table 1 describes the parameters for LUN properties.
Confirm the modification of properties for the LUN.
1. Click OK.
  The Information dialog box is displayed indicating that the operation succeeded.
2. Click OK. The properties for the LUN are modified.
Check whether data is written to disks.
1. Wait 5 to 10 minutes and log in to the storage system using the CLI.
2. Log in to developer Mode
3. Run the showcachelun -lun [LUN ID] command. Parameter [LUN ID] is the ID of LUN to be modified.
4. Ensure the value of drity page count is 0.
Go to the Modify LUN dialog box.
1. Log in to the ISM. In the navigation tree, choose All Devices > SN_XX > Storage Resources > LUNs, where SN_XX indicates a storage system.
2. In the function pane, select the desired LUN.
3. Click Modify.
  The Modify LUN dialog box is displayed.
Modify Write Policy of the LUN to Write Back/Mirroring. Table 1 describes the parameters for LUN properties.
Confirm the modification of properties for the LUN.
1. Click OK.
  The Information dialog box is displayed indicating that the operation succeeded.
2. Click OK. The properties for the LUN are modified.
You are advised to perform this operation during off-peak hours.
If you have any questions, please contact technical support engineers for further handling.

**Table 1** Parameters for LUN properties
Parameter	Description	Value
Write Policy	Indicates the data write mode of a LUN.	Write Through: The storage system writes data onto the cache and disks on the storage system simultaneously upon receiving a data write request sent by the application server. Write Back/Mirroring: The storage system writes data onto the local and the peer cache simultaneously upon receiving a data write request sent by the application server. Write Back/No Mirroring: The storage system writes data only onto the local cache upon receiving a data write request sent by the application server. Write Back Mandatory/Mirroring: The storage system forcibly writes data onto the local and the peer cache simultaneously when encountering certain faults such as overheating or insufficient power supply from BBUs. Write Back Mandatory/No Mirroring: The storage system forcibly writes data onto the local cache when encountering certain faults such as overheating or insufficient power supply from BBUs.