Method used to modify the LUN write back policy

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1. If write policy is changed to write back without mirroring or mandatory write back without mirror, the cache data in the LUN may be lost. Perform this operation with caution.

2. Go to the Modify LUN dialog box.
In the ISM navigation tree, choose All Devices > SN_XX > Storage Resources > LUN (SN_XX is the name of the target storage system).
In the right function pane, select the LUN you want to modify.
Click Modify.
The Modify LUN dialog box is displayed.
Modify the basic and advanced attributes of the LUN.

Other related questions:
Feature of the LUN write back policy
1. After data is written to the controller cache, acknowledgment information is sent to the upper-layer host, and the upper-layer host starts to write the next data. 2. The reliability of data written back is reduced and the performance is high.

Feature of the LUN write back with mirroring policy
Write back with mirroring: Data is written to the local cache and peer cache at the same time. Write back with mirroring: features higher write performance than write through but lower write performance than write back without mirroring. This policy does not compromise the read performance. Therefore, write back with mirroring applies to the applications that require high write performance and high reliability.

Feature of the LUN write back without mirroring policy
Write back without mirroring: only writes data to the local cache. Write back without mirroring: features optimal write performance but poor reliability. Write back without mirroring applies to applications that require high write performance but low reliability.

Method used to plan LUN read/write policies
You can plan LUN read/write policies as follows: 1. Planning the write policy You can select the following write policies during LUN creation: write through, write back and mirroring, and write back without mirroring, mandatory write back and mirroring, and mandatory write back without mirroring. The following is the differences among write policies: Write through: writes data to disks. Each write operation must access the disk, contributing to low performance but high reliability. Write back: writes data to the cache and then write data to disks when there are idle host I/Os. Each write operation does not access the disk with high performance but low reliability. Write back and mirroring: writes data to both the local cache and peer cache simultaneously. Write back without mirroring: writes data to the local cache. Mandatory write back and mirroring: Storage devices must write data to the local cache and peer cache simultaneously. Mandatory write back without mirroring: Storage device must write data to the local cache. 2. Planning prefetch policies You can select the following prefetch polices: intelligent prefetch, constant prefetch, variable prefetch, and non-prefetch.

Method used to modify the LUN prefetch policy
Go to the Modify LUN dialog box. In the ISM navigation tree, choose All Devices > SN_XX > Storage Resources > LUN (SN_XX is the name of the target storage system). In the right function pane, select the LUN you want to modify. Click Modify. The Modify LUN dialog box is displayed. Modify the basic and advanced attributes of the LUN.

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