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Basic Storage Service Configuration Guide for Block

OceanStor V5 Series V500R007

This document is applicable to OceanStor 5110 V5, 5300 V5, 5500 V5, 5600 V5, 5800 V5, 6800 V5, 5300F V5, 5500F V5, 5600F V5, 5800F V5, 6800F V5, 18500 V5, 18800 V5, 18500F V5, and 18800F V5. It describes the basic storage services and explains how to configure and manage them.
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I/O Processing Procedure Between an Application Server and a Storage System

I/O Processing Procedure Between an Application Server and a Storage System

This section describes how I/Os are processed in scenarios where UltraPath is enabled and the round-robin load balancing algorithm is used to implement cross-controller load balancing.

Scenario 1: An Application Server Sends a Write I/O Request to a LUN When a Storage System Has Only One Controller Enclosure

Figure 2-3 How a write I/O request is processed when a storage system has only one controller enclosure

Scenario 2: An Application Server Sends a Read I/O Request to a LUN When a Storage System Has Only One Controller Enclosure

Figure 2-4 How a read I/O request is processed when a storage system has only one controller enclosure

Scenario 3: An Application Server Sends a Write I/O Request to a LUN Whose Working and Owning Controllers Are the Same When a Storage System Has Multiple Controller Enclosures

Figure 2-5 How a write I/O request is processed when a storage system has multiple controller enclosures and the working and owning controllers of the target LUN are the same

Scenario 4: An Application Server Sends a Read I/O Request to a LUN Whose Working and Owning Controllers Are the Same When a Storage System Has Multiple Controller Enclosures

Figure 2-6 How a read I/O request is processed when a storage system has multiple controller enclosures and the working and owning controllers of the target LUN are the same

Scenario 5: An Application Server Sends a Write I/O Request to a LUN Whose Working and Owning Controllers Are Different When a Storage System Has Multiple Controller Enclosures

When the working and owning controllers of a LUN are different, I/O requests to the LUN are forwarded by the working controller to the owning controller and then processed by the owning controller.

Figure 2-7 How a write I/O request is processed when a storage system has multiple controller enclosures and the working and owning controllers of the target LUN are different

Scenario 6: An Application Server Sends a Read I/O Request to a LUN Whose Working and Owning Controllers Are Different When a Storage System Has Multiple Controller Enclosures

When the working and owning controllers of a LUN are different, I/O requests to the LUN are forwarded by the working controller to the owning controller and then processed by the owning controller.

Figure 2-8 How a read I/O request is processed when a storage system has multiple controller enclosures and the working and owning controllers of the target LUN are different

Scenario 7: An Application Server Sends a Write I/O Request to a LUN Whose Working and Owning Controllers Are the Same When a Storage System Has Multiple Controller Enclosures (18000 and 18000F Series Storage Systems)

Figure 2-9 How a write I/O request is processed when a storage system has multiple controller enclosures and the working and owning controllers of the target LUN are the same

Scenario 8: Application Server Sends a Read I/O Request to a LUN Whose Working and Owning Controllers Are the Same When a Storage System Has Multiple Controller Enclosures (18000 and 18000F Series Storage Systems)

Figure 2-10 How a read I/O request is processed when a storage system has multiple controller enclosures and the working and owning controllers of the target LUN are the same

Scenario 9: An Application Server Sends a Write I/O Request to a LUN Whose Working and Owning Controllers Are Different When a Storage System Has Multiple Controller Enclosures (18000 and 18000F Series Storage Systems)

When the working and owning controllers of a LUN are different, I/O requests to the LUN are forwarded by the working controller to the owning controller and then processed by the owning controller.

Figure 2-11 How a write I/O request is processed when a storage system has multiple controller enclosures and the working and owning controllers of the target LUN are different

Scenario 10: An Application Server Sends a Read I/O Request to a LUN Whose Working and Owning Controllers Are Different When a Storage System Has Multiple Controller Enclosures (18000 and 18000F Series Storage Systems)

When the working and owning controllers of a LUN are different, I/O requests to the LUN are forwarded by the working controller to the owning controller and then processed by the owning controller.

Figure 2-12 How a read I/O request is processed when a storage system has multiple controller enclosures and the working and owning controllers of the target LUN are different

Scenarios Where the LUN Write Mode Becomes Write Through

The write mode of LUNs in a storage system is write back by default. However, the write mode will become write through in the event of a fault.

Table 2-1 Scenarios where the write mode of LUNs changes from write back to write through and recommended actions

Symptom

Scenario

Impact and Recommended Action

The temperature of a controller exceeds the upper limit.

  • If the Controller Enclosure Temperature Exceeds The Upper Limit alarm is generated due to an exception in the equipment room temperature or the internal components of a storage system, LUNs remain in write back mode for a specified period of time (192 hours by default). If the alarm persists after the specified period of time, the mode changes to write through.
  • If the Controller Enclosure Temperature Exceeds The Upper Limit alarm is generated due to a fault on a single controller of a controller enclosure, LUNs remain in write back mode for a specified period of time (1 hour by default). If the alarm persists after the specified period of time, the mode changes to write through.
NOTE:

If the Controller Enclosure Temperature Is Far Beyond The Upper Limit alarm is generated in a storage system, the storage system will automatically power off.

  • Impact

    The write mode of all LUNs belonging to the controller enclosure changes to write through after the specified period of time.

  • Recommended action

    Check the external refrigerating system, fan modules, and air channels to locate the cause of the over-temperature alarm and rectify faults.

Backup battery units (BBUs) on a controller enclosure malfunction.

  • Dual-controller storage system: If two BBUs malfunction and an alarm is generated, the write mode changes from write back to write through.
  • Four-controller storage system: If two or more BBUs malfunction and an alarm is generated, the write mode changes from write back to write through.
  • Impact

    The write mode of all LUNs belonging to the controller enclosure changes to write through.

  • Recommended action
    • Check whether the BBUs are properly installed.
    • Check whether the BBUs are faulty and replace them if necessary.
    • Check whether the charge of the BBUs is insufficient. If the power of the BBUs is insufficient, wait until the BBUs are fully charged.

The coffer disks of a controller enclosure malfunction.

  • Dual-controller storage system: If two coffer disks break down, the write mode changes from write back to write through.
  • Four-controller storage system: If all coffer disks of controllers A and B or controllers C and D break down (the controllers in the first row are controllers A and B and the controllers in the second row are controllers C and D), the write mode changes from write back to write through.
  • Impact

    The write mode of all LUNs belonging to the controller enclosure changes to write through.

  • Recommended action

    Check whether the coffer disks are faulty and replace them if necessary.

A controller malfunctions.

If a single controller malfunctions, LUNs remain in write back mode for a specified period of time (192 hours by default). If the fault is not rectified within this period, the write mode changes from write back to write through.

  • Impact

    The write mode of all LUNs belonging to the controller enclosure becomes write through if the fault persists after 192 hours.

  • Recommended action
    • Replace the faulty controller during off-peak hours and within the 192 hour period after the malfunction.
    • If a spare part is unavailable during the write back protection period, extend the time after assessing risks to prevent write through from adversely affecting service performance.

The remaining capacity of a storage pool is smaller than the reserved capacity.

An alarm is generated, indicating that the capacity usage of a storage pool exceeds the threshold and reminding you to expand the storage pool.

  • Impact

    The write mode of thin LUNs and thick LUNs with value-added features changes from write back to write through.

  • Recommended action

    Expand the storage pool.

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Updated: 2019-08-30

Document ID: EDOC1000181506

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