Checking the Performance Impacts of Internal Transactions and Value-Added Features

Internal transactions refer to the work completed in the background in response to user operations, for example, reconstructing data upon a disk failure, data balancing upon capacity expansion, and global garbage collection. In addition to numerous metadata operations, internal transactions and value-added features may generate a large number of non-host I/Os. Therefore, host services processed by the storage system are affected.

Before diagnosing a performance problem, check whether there are internal transactions or value-added features. Examples of these are as follows:

• Precopy and reconstruction
  • Precopy: The precopy technique enables the storage system to regularly check the status of hardware. If a disk may fail, the storage system will migrate the data from the disk to mitigate data loss.
  • Reconstruction: If a disk fails, the reconstruction function restores data to a newly allocated hot spare space based on a RAID redundancy mechanism, leading to a large amount of RAID computing and data copying.
    Data copy tasks are generated during the precopy or reconstruction. If a large amount of data needs to be copied, the service performance is adversely affected. Therefore, before conducting a performance test, run the related command on the CLI to check whether these tasks exist already.

    admin:/>show disk_domain task disk_domain_id=0 

    Disk Domain ID : 0 

    Type : Reconstruct 

    Disk Enclosure : DAE101 

    Disk Slot : 23 

    Data Size : 17.625GB 

    Data Finished Size : 1.375GB 

    Remain Time : 0Day(s) 1Hour(s) 26Minute(s) 4Second(s) 

    Progress : 7%

If disk domains are already engaged in precopy or reconstruction, their progress can be viewed. However, if these tasks are not currently engaged, a message is displayed indicating that the command is successfully executed.

• Migration

  SmartMigration supports LUN migration within or between storage devices. Migration involves a large number of data read, write, and copy operations, leading to performance deterioration. A migration speed can be specified. A higher speed has a greater impact on host I/Os.

• Other value-added features

  Value-added features such as snapshot and remote replication cause extra overheads and prolong the I/O processing. For details about the impact of value-added features on host performance, see the corresponding feature guide.