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OceanStor 2200 V3 and 2600 V3 Storage System V300R005 SmartVirtualization Feature Guide 07

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Huawei uses machine translation combined with human proofreading to translate this document to different languages in order to help you better understand the content of this document. Note: Even the most advanced machine translation cannot match the quality of professional translators. Huawei shall not bear any responsibility for translation accuracy and it is recommended that you refer to the English document (a link for which has been provided).
Creating an eDevLUN Without Masquerading Properties

Creating an eDevLUN Without Masquerading Properties

After an eDevLUN is created, you can map it to an application server or configure value-added services for it. eDevLUNs reside in storage pools of the local storage system.

Prerequisites

  • The remote LUNs mapped by the heterogeneous storage system have been added to the LUN list by automatic scanning.
  • External LUNs are in normal state.
  • Number of LUNs (including local LUNs and eDevLUNs) in a storage pool = Available capacity of the storage pool/512 MB. Before creating an eDevLUN, make an appropriate plan to ensure that the storage pool has sufficient capacity for the eDevLUN.
    • If you need to configure one of the remote replication, SmartMigration, HyperMirror, snapshot, and HyperMetro features for an eDevLUN, you must reserve a certain amount of capacity in the local storage pool for storing metadata generated by that feature. Reserved capacity = External LUN capacity x 5‰.
    • If you need to configure two or more of the remote replication, SmartMigration, HyperMirror, snapshot, and HyperMetro features for an eDevLUN, you must reserve a certain amount of capacity in the local storage pool. Reserved capacity = External LUN capacity x 1%.
    • If you want to configure HyperSnap and HyperReplication/A for eDevLUNs, reserve some space in the local storage pool to save copy-on-write (COW) data. The reserved capacity ranges from 20% to 30% of the external LUN capacity.
    • If you want to configure HyperReplication/S and HyperMetro for eDevLUNs, reserve some space in the local storage pool to save incremental data generated after replication fault occurs. The reserved capacity is 10% of the external LUN capacity.
  • If the external LUNs have been mapped to a host cluster, shut down the cluster following standard procedures and ensure that no cluster information remains on the external LUNs. Then map the external LUNs to the local storage system. Otherwise, the external LUNs cannot be hosted by the local storage system normally, affecting services on the LUNs.

Context

By default, the write policy of an eDevLUN is write through. After creating an eDevLUN, you can modify its write policy on the management page of LUNs.

Precautions

After creating an eDevLUN for an external LUN, do not map the external LUN to other hosts or storage systems to avoid data inconsistency.

Procedure

  1. Log in to DeviceManager.
  2. Choose Data Protection > Remote Device.
  3. Select the heterogeneous storage system where the external LUN resides. In the function pane, click the Remote LUN tab.
  4. Click Create eDevLUN.

    The Create eDevLUN dialog box is displayed.

  5. Create an eDevLUN.
    1. Select a storage pool for the eDevLUN to be created.

      NOTE:
      • When eDevLUNs are created, the system automatically generates a default name for each eDevLUN. You can modify the default name.
      • If no storage pool is available, click Create to create a new storage pool.

    2. Set LUN Masquerading to No Masquerading.

      The WWN of the non-masqueraded eDevLUN is different from that of the external LUN, the application server will regard the eDevLUN and external LUN as two different LUNs. To avoid data inconsistency as the application server may write different service data to the eDevLUN and the external LUN after the takeover, you need to cancel the mapping between the external LUN and the application server in the third-party storage system.

    3. In the list, select a remote LUN that you want to configure as an eDevLUN.
    4. Click Advanced and set the advanced properties of the eDevLUN. After setting the advanced properties, click OK to save the configuration and exit.

      Table 2-3 lists the advanced property parameters of an eDevLUN.

      Table 2-3  Advanced property parameters of an eDevLUN

      Parameter

      Description

      Value

      Read Policy

      Data read policy of an eDevLUN.

      The system supports the following three read policies:
      • Resident: Applies to services featuring random data access, ensuring that data can be cached as long as possible to improve the read hit ratio.
      • Default: Applies to regular services, striking a balance between the hit ratio and disk access performance.
      • Recycle: Applies to services featuring sequential data access, releasing cache resources for other services as soon as possible.

      [Value range]

      Possible values are Resident, Default, and Recycle.

      [Example]

      Default

      [Default value]

      Default

      Write Policy

      Data write policy of an eDevLUN.

      The system supports the following three write policies:
      • Resident: Applies to services featuring random data access, ensuring that data can be cached as long as possible to improve the write hit ratio.
      • Default: Applies to regular services, striking a balance between the hit ratio and disk access performance.
      • Recycle: Applies to services featuring sequential data access, releasing cache resources for other services as soon as possible.
      NOTE:

      If the change lun command is executed on the CLI to modify write_policy to write_through, this parameter write_through becomes invalid.

      [Value range]

      Possible values are Resident, Default, and Recycle.

      [Example]

      Default

      [Default value]

      Default

      Prefetch Policy

      Read mode of an eDevLUN. When reading data, an eDevLUN prefetches required data from disks to the cache in advance according to a preset policy.
      • No prefetch: The storage system reads data according to the prefetch length specified in the I/O request.

        As a low read hit ratio may lead to performance degradation, No prefetch is recommended for random read services.

      • Intelligent prefetch: Intelligent prefetch analyzes whether the requested data is sequential. If it is, the data following the currently requested data is prefetched from disks to the cache to improve the cache hit ratio. If data is randomly read, no prefetch is performed and the required data is read from disks.

        This policy applies to a scenario where sequential reads and random reads coexist or a scenario where you cannot determine data reads to be sequential or random.

      • Constant prefetch: A constant length of data is read from disks every time when the cache reads data from the disks. The length is user-definable, ranging from 0 to 1024.

        This policy applies to sequential read applications with fixed-size data, for example, color ring back tone (CRBT) and multi-user streaming media video on demand (VoD) initiated by users at the same bit rate.

      • Variable prefetch: A variable length of data is read from disks every time when the cache reads data from disks. The length is a multiple of that specified in the host I/O request. The multiple is user-defined, ranging from 0 to 1024.

        This policy applies to sequential read applications with variable-size data or to multi-user concurrent read applications with an unknown data prefetch amount, for example, streaming media requests initiated by multiple users at different bit rates.

      [Value range]

      Possible values are No prefetch, Intelligent prefetch, and Constant prefetch, and Variable prefetch.

      [Example]

      Intelligent prefetch

      [Default value]

      Intelligent prefetch

  6. Confirm the creation of the eDevLUN.
    1. Click OK.

      The Execution Result dialog box is displayed indicating that the operation succeeded.

    2. Click Close.

Follow-up Procedure

An eDevLUN is created successfully if Used or Not of the corresponding remote LUN in the lower function pane is Yes. Choose Provisioning > LUN to view and manage the eDevLUN.
NOTE:

Because WWN rules vary according to different vendors, the WWN (that is displayed) of an eDevLUN is different from that of an external LUN after the external LUN is hosted on the local storage system and the eDevLUN is created. (For some vendors, the WWN of the external LUN may be displayed as the UUID.)

Before configuring a value-added feature for an eDevLUN without masquerading properties, comply with the following principles to modify the write policy of the eDevLUN:
NOTE:

Method of modifying the write policy of an eDevLUN: Choose Provisioning > LUN. Select the eDevLUN whose write policy you want to modify and click Properties. On the Properties of LUN page that is displayed, click Advanced.

  • If you want to configure the HyperMirror feature for the eDevLUN, set the write policy of the eDevLUN to Write through and the write policy of the mirror copy generated on the local storage system to Write back to ensure data consistency between the heterogeneous storage system and the local storage system.
  • If the SmartMigration feature is configured for the eDevLUN, set the write policy of the eDevLUN to Write through to ensure data consistency between the heterogeneous storage system and local storage system.
  • If the Snapshot, Remote Replication or HyperMetro is configured for the eDevLUN, set the write policy of the eDevLUN to Write back to ensure performance of the local storage system.
  • If HyperMirror and Snapshot are configured simultaneously for the eDevLUN, or HyperMirror and Remote Replication are configured simultaneously for it, set the write policy of the eDevLUN to Write back.
  • If no value-added feature is configured for the eDevLUN, you do not need to modify its write policy. Keep the default Write through policy.
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Updated: 2018-12-29

Document ID: EDOC1000106155

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