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Huawei SAN Storage Host Connectivity Guide for Windows

HUAWEI SAN Storage Host Connectivity Guide for Windows Servers
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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).
Multipath Connectivity

Multipath Connectivity

UltraPath

UltraPath is a Huawei-developed multipathing software. It can manage and process disk creation/deletion and I/O delivery of operating systems.

UltraPath provides the following functions:

  • Masking of redundant LUNs

    In a redundant storage network, an application server with no multipathing software detects a LUN on each path. Therefore, a LUN mapped through multiple paths is mistaken for two or more different LUNs. UltraPath installed on the application server masks redundant LUNs on the operating system driver layer to provide the application server with only one available LUN, the virtual LUN. In this case, the application server only needs to deliver data read and write operations to UltraPath. UltraPath then masks the redundant LUNs, and writes data into LUNs without damaging other data.

  • Optimum path selection

    In a multipath environment, the owning controller of the LUN on the storage system mapped to an application server is the prior controller. With UltraPath, an application server accesses the LUN on the storage system through the prior controller, thereby obtaining the highest I/O speed. The path to the prior controller is the optimum path.

  • Failover and failback
    • Failover

      When a path fails, UltraPath fails over its services to another functional path.

    • Failback

      UltraPath automatically delivers I/Os to the first path again after the path recovers from the fault.

  • I/O Load balancing

    UltraPath provides load balancing within a controller and across controllers.

    • For load balancing within a controller, I/Os poll among all the paths of the controller.
    • For load balancing across controllers, I/Os poll among the paths of all these controllers.
  • Path test

    UltraPath tests faulty and idle paths:

    • Faulty paths

      UltraPath frequently tests faulty paths to detect the path recovery as soon as possible.

    • Idle paths

      UltraPath tests idle paths to identify potentially faulty paths early on, preventing unnecessary I/O retries. The test frequency is kept low to minimize impact on service I/Os.

MPIO

Windows Microsoft Multi-Path IO (MPIO) allows storage vendors to develop multipathing solutions that contain the hardware-specific information needed to optimize connectivity with storage systems. MPIO can be used independently. This software helps balance loads among multiple paths, and implement path selection and failover between storage systems and hosts.

MPIO supports the following policy settings:

  • Failover Only

    This policy does not perform load balancing. This policy uses a single active path, and the rest of the paths are standby paths. The active path is used for sending all I/Os. If the active path fails, then one of the standby paths is used. When the failed path is reactivated or reconnected, the standby path that was activated returns to standby.

  • Round Robin

    This load balancing policy allows the Device Specific Module (DSM) to use all available paths for MPIO in a balanced way. This is the default policy that is chosen when the storage controller follows the active-active model and the management application does not specifically choose a load balancing policy.

  • Round Robin with Subset

    This load balancing policy allows the application to specify a set of paths to be used in a round robin fashion, and with a set of standby paths. The DSM uses paths from a primary path pool for processing requests as long as at least one of the paths is available. The DSM uses a standby path only when all the primary paths fail. For example, given 4 paths: A, B, C, and D, paths A, B, and C are listed as primary paths and D is the standby path. The DSM chooses a path from A, B, and C in round robin fashion as long as at least one of them is available. If all three paths fail, the DSM uses D, the standby path. If paths A, B, or C become available, the DSM stops using path D and switches to the available primary paths.

  • Least Queue Depth

    This load balancing policy sends I/O down the path with the fewest currently outstanding I/O requests. For example, consider that there is one I/O sent to LUN 1 on Path 1, and the other I/O is sent to LUN 2 on Path 1. The cumulative outstanding I/O on Path 1 is 2, and on Path 2 is 0. Therefore, the next I/O for either LUN will process on Path 2.

  • Weighed Paths

    This load balancing policy assigns a weight to each path. The weight indicates the relative priority of a given path. The larger the number, the lower ranked the priority. The DSM chooses the least-weighted path from among the available paths.

  • Least Blocks

    This load balancing policy sends I/O down the path with the least number of data blocks currently being processed. For example, consider that there are two I/Os: one is 10 bytes and the other is 20 bytes. Both are in process on Path 1, and there are no outstanding I/Os on Path 2. The cumulative outstanding amount of I/O on Path 1 is 30 bytes. On Path 2, it is 0. Therefore, the next I/O will process on Path 2.

ALUA

  • ALUA definition

    Asymmetric Logical Unit Access (ALUA) is a multi-target port access model. In a multipathing state, the ALUA model provides a way of presenting active/passive LUNs to a host and offers a port status switching interface to switch over the working controller. For example, when a host multipathing program that supports ALUA detects a port status change (the port becomes unavailable) on a faulty controller, the program will automatically switch subsequent I/Os to the other controller.

  • Support by Huawei storage

    Old-version Huawei storage supports ALUA only in dual-controller configuration, but not in multi-controller or HyperMetro configuration.

    New-version Huawei storage supports ALUA in dual-controller, multi-controller, and HyperMetro configurations.

    Table 2-2 defines old- and new-version Huawei storage.

Table 2-2 Old- and new-version Huawei storage

Storage Type

Version

Remarks

Old-version Huawei storage (namely, storage that does not support multi-controller ALUA or ALUA HyperMetro)

T V1, T V2, 18000 V1, V300R001, V300R002, V300R003C00, V300R003C10, V300R005, and Dorado V300R001C00

-

New-version Huawei storage (namely, storage that supports multi-controller ALUA and ALUA HyperMetro)

V300R003C20, V300R006C00, V500R007C00, Dorado V300R001C01, and later versions

V300R003C20: refers to only V300R003C20SPC200 and later versions.

V300R006C00: refers to only V300R006C00SPC100 and later versions.

Dorado V300R001C01: refers to only V300R001C01SPC100 and later versions.

  • ALUA impacts

    ALUA is applicable to a storage system that has only one prior LUN controller. All host I/Os can be routed through different controllers to the working controller for execution. ALUA will instruct the hosts to deliver I/Os preferentially from the LUN working controller, thereby reducing the I/O routing-consumed resources on the non-working controllers.

    If all I/O paths of the LUN working controller are disconnected, the host I/Os will be delivered only from a non-working controller and then routed to the working controller for execution.

  • Suggestions for using ALUA on Huawei storage

    To prevent I/Os from being delivered to a non-working controller, you are advised to ensure that:

    • LUN home/working controllers are evenly distributed on storage systems so that host service I/Os are delivered to multiple controllers for load balancing.
    • Hosts always try the best to select the optimal path to deliver I/Os even after an I/O path switchover.
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Updated: 2019-08-22

Document ID: EDOC1000150159

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