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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).
Working Principle

Working Principle

SmartVirtualization allows external LUNs in heterogeneous storage systems to provide physical storage space for the OceanStor 2200 V3/2600 V3 storage system.

Related Concepts

  • Data organization
    A local storage system uses a storage virtualization technology, and each LUN in the local storage system consists of a metadata volume and a data volume.
    • A metadata volume records data storage locations.
    • A data volume saves users' data.
  • Local storage system

    A local storage system refers to OceanStor 2200 V3/2600 V3 storage system.

  • Heterogeneous storage system

    In SmartVirtualization, a heterogeneous storage system can be either a storage system manufactured by another mainstream vendor or a Huawei storage system of another model. For details, see Table 1-2. A heterogeneous storage system is displayed as a remote device on the DeviceManager.

  • External LUN

    A LUN in a heterogeneous storage system, which is displayed as a remote LUN on the DeviceManager.

  • eDevLUN

    The local storage system organizes external LUNs into raw storage devices in storage pools based on a certain data organization form. A raw storage device is called an eDevLUN that consist of a metadata volume and data volume. The physical space occupied by an eDevLUN in the local storage system is merely the storage space needed by the metadata volume. Application servers can use eDevLUNs to access data on external LUNs in a heterogeneous storage system and configure value-added features such as snapshot, remote replication, SmartMigration, and HyperMirror for the eDevLUNs.

  • LUN masquerading

    For the OceanStor 2200 V3/2600 V3 storage system, when LUNs in a heterogeneous storage system are encapsulated as eDevLUNs, you can set the LUN masquerading properties. Application servers identity eDevLUNs as LUNs in a heterogeneous storage system, the (World Wide Name) WWN and host LUN ID of an eDevLUN identified by a host are the same as those of the corresponding external LUN. By setting the masquerading properties of eDevLUNs, online LUN takeover can be implemented.

  • Hosting

    LUNs in a heterogeneous storage system are mapped to a local storage system for use and management.

Relationship Between an eDevLUN and an External LUN

An eDevLUN consists of a data volume and a metadata volume.
  • A data volume is a logical abstract object of an external LUN. Physical space needed by a data volume is provided by a heterogeneous storage system rather than the local storage system.
  • A metadata volume manages the locations of data stored on an eDevLUN. Physical space needed by a metadata volume is provided by the local storage system, and a metadata volume only occupies a small amount of space. If no value-added features are configured for eDevLUNs, each eDevLUN consumes about 130 MB of space in the storage pool of the local storage system.
    NOTE:

    If value-added features are configured for eDevLUNs, each eDevLUN, like any other local LUNs, occupies local storage system space to store the metadata of value-added features. Properly plan storage space before creating eDevLUNs to ensure that value-added features can work correctly.

An eDevLUN created in the local storage system has a one-to-one mapping relationship with an external LUN created in the heterogeneous storage system. An application server accesses an external LUN by reading and writing data to an eDevLUN.

Figure 1-1 illustrates the relationship between an eDevLUN and an external LUN.
Figure 1-1  Relationship between an eDevLUN and an external LUN

Data Read and Write Processes

With the use of SmartVirtualization, an application server can read and write data to an external LUN in a heterogeneous storage system through the local storage system. The process of reading and writing data to an external LUN is similar to the process of reading and writing data to a LUN in the local storage system.

  • Data read process
    After an external LUN in a heterogeneous storage system is hosted using SmartVirtualization, hotspot data on the external LUN is cached to the cache of the eDevLUN. When an application server sends a request to read data from the external LUN, priority is given to the data on the eDevLUN in the local storage system. If the requested data cannot be hit in the eDevLUN, data is read from the external LUN. Figure 1-2 shows the data read process.
    Figure 1-2  Data read process

  • Data write process
    After an external LUN in a heterogeneous storage system is hosted using SmartVirtualization, the corresponding eDevLUN supports write back and write through policies, as other LUNs in the local storage system do. Figure 1-3 shows the write process.
    • Write back: After an application server sends a data write back request, the local storage system returns an I/O write response to the application server as soon as the data block is written to the local storage system. Then, the local storage system writes the data block to the heterogeneous storage system.
    • Write through: After an application server sends a data write through request, the data block is written to the local storage system, and then from the local storage system to the heterogeneous storage system. After the data block is successfully written to the heterogeneous storage system, the heterogeneous storage system returns an I/O write response to the local storage system which then returns an I/O write response to the application server.
    Figure 1-3  Data write process

    The default LUN Write Policy of eDevLUNs is Write through. After creating an eDevLUN, you can set its write policy by configuring its properties. The impact on the performance of the heterogeneous storage system varies depending on different write policies.
    • The write through policy is the most secure write policy because data is ultimately stored in the heterogeneous storage system. If the load capacity of the heterogeneous storage system cannot tolerate the write speed, the write through policy is recommended.
    • If the load capacity of the heterogeneous storage system cannot tolerate the write speed, the write back policy will adversely affect the local storage system performance. eDevLUNs supports multiple value-added features. To ensure performance after the value-added features are used, you are advised to modify the write policy of eDevLUNs. For details, see "Follow-up Procedure" in "Creating an eDevLUN Without Masquerading Properties" and "Creating an eDevLUN With Masquerading Properties".
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Updated: 2018-12-29

Document ID: EDOC1000106155

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