Multipath Connectivity

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 that masks the redundant LUNs, and properly writes data into LUNs without damaging other data.

• Optimum path selection

  In a multipath environment, an application server with UltraPath accesses a LUN on the storage system through an optimum path, thereby obtaining the highest I/O speed.

• 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 the following paths:

  • Faulty paths

    UltraPath tests faulty paths with a high frequency to detect the path recover as soon as possible.

  • Idle paths

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

MPIO is the AIX native multipathing software. It can take over Huawei storage after Huawei-developed storage ODM library software AIX ODM for MPIO is installed. AIX ODM for MPIO offers basic functions such as shielding physical disks and generating virtual disks. However, it cannot switch the working controller for a LUN. If an AIX application server and a Huawei storage device are connected by redundant links and SAN boot needs to be performed between them, AIX ODM for MPIO helps the server to identify the Huawei storage device and perform SAN boot operations on identified Huawei disks.

Dynamic Multipathing (DMP), integrated with Veritas Volume Manager (VxM) of Symantec Storage Foundation, implements failover and balances I/Os across multiple available paths between hosts and storage systems, thereby improving performance and availability. DMP applies to storage systems from various vendors.

• 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.

• ALUA impacts

  ALUA is mainly 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.